ICU-22532 Use previous Ubuntu version for ICU4C in GH Actions CI for now

.github/workflows/icu4c.yml

@@ -29,7 +29,7 @@ jobs:
 
   # ICU4C docs build using doxygen..
   icu4c-docs-build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -52,7 +52,7 @@ jobs:
   #
   # Invokes test/hdrtst to check public headers compliance.
   gcc-debug-build-and-test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -75,7 +75,7 @@ jobs:
   # (FORCE guards make this tool pass but won't compile to working code.
   # See the testtagsguards.sh script for details.)
   clang-release-build-and-test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -117,7 +117,7 @@ jobs:
         build_option:
          [ --enable-static, --enable-static --disable-shared ]
          # --disable-shared has a build problem.
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
 
@@ -133,7 +133,7 @@ jobs:
 
   # Out of source build with gcc 10, c++14, and extra warnings; executes icuinfo.
   gcc-10-stdlib17:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -154,7 +154,7 @@ jobs:
 
   # Clang Linux with address sanitizer.
   clang-asan:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -168,7 +168,7 @@ jobs:
           LDFLAGS: -fsanitize=address
   # Clang Linux with undefined-behavior sanitizer.
   clang-ubsan:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -183,7 +183,7 @@ jobs:
           LDFLAGS: -fsanitize=undefined -fsanitize=alignment -fno-sanitize-recover=undefined,alignment
   # Control Flow Integrity.
   clang-cfi:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -202,7 +202,7 @@ jobs:
 
   # Clang Linux with thread sanitizer.
   clang-tsan:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -232,7 +232,7 @@ jobs:
 
   # Run ICU4C tests with stubdata.
   run-with-stubdata:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
 
@@ -275,7 +275,7 @@ jobs:
 
   # Test U_CHARSET_IS_UTF8
   u-charset-is-utf8-test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: |
@@ -285,7 +285,7 @@ jobs:
 
   # Test U_OVERRIDE_CXX_ALLOCATION-is-0-test
   u-override-cxx-allocation-is-0-test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: |
@@ -296,7 +296,7 @@ jobs:
 
   # Test LSTM
   lstm-test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: |
@@ -307,7 +307,7 @@ jobs:
 
   # Test adaboost
   adaboost-test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: |
@@ -318,7 +318,7 @@ jobs:
 
   # Build and run testmap
   testmap:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: |
@@ -331,28 +331,28 @@ jobs:
 
   # Copyright scan
   copyright-scan:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: perl tools/scripts/cpysearch/cpyscan.pl
 
   # Check compilation of internal headers.
   internal-header-compilation:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: cd icu4c/source; test/hdrtst/testinternalheaders.sh
 
   # Check source files for valid UTF-8 and for absence of BOM.
   valid-UTF-8-and-no-BOM-check:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - run: tools/scripts/icu-file-utf8-check.py
 
   # Run unit tests with UCONFIG_NO_XXX variations.
   uconfig-unit-tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       # "fail-fast: false" lets other jobs keep running even if the test breaks in some other uconfig.
       fail-fast: false
@@ -398,7 +398,7 @@ jobs:
 
   # Run header tests with UCONFIG_NO_XXX variations.
   uconfig-header-tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       # "fail-fast: false" lets other jobs keep running even if the test breaks in some other uconfig.
       fail-fast: false
@@ -448,7 +448,7 @@ jobs:
 
   # Build Unicode update tools
   unicode-update-tools:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@v3
     - uses: bazelbuild/setup-bazelisk@v2
@@ -487,7 +487,7 @@ jobs:
 
 # Build and run ICU4C samples
   icu4c-test-samples:
-      runs-on: ubuntu-latest
+      runs-on: ubuntu-20.04
       steps:
       - uses: actions/checkout@v3
 
@@ -512,7 +512,7 @@ jobs:
 
   # https://unicode-org.github.io/icu/processes/release/tasks/integration.html#verify-that-icu4c-tests-pass-without-collation-rule-strings
   icu4c-without-collation-rule-strings:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - name: Install hjson dependency
@@ -552,7 +552,7 @@ jobs:
   
   # https://unicode-org.github.io/icu/processes/release/tasks/healthy-code.html#test-uconfig_no_conversion
   icu4c-uconfig-no-conversion:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
       - name: Set UCONFIG_NO_CONVERSION and configure ICU4C