ICU-22384 Limit execution of performance tests

Run the tests only on the main branch of the unicode-org/icu repository. This avoids diluting the performance charts with performance results from the maintenance branches. Also, the performance tests won't execute on forked directories anymore, on which they fail after execution anyway, thus using GitHub resources without purpose.

.github/workflows/icu_merge_ci.yml

@@ -39,6 +39,8 @@ jobs:
 
   # Compile libraries used by all ICU4C performance tests.
   icu4c-store-perf-libs:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -59,6 +61,8 @@ jobs:
 
   # Assorted ICU4C performance tests
   icu4c-performance-tests:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     needs: icu4c-store-perf-libs
     strategy:
       fail-fast: false
@@ -109,6 +113,8 @@ jobs:
 
   # Assorted ICU4C performance tests using data files
   icu4c-performance-tests-with-files:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     needs: icu4c-store-perf-libs
     strategy:
       fail-fast: false
@@ -179,6 +185,8 @@ jobs:
 
   # String search performance test
   icu4c-strsrchperf:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     needs: icu4c-store-perf-libs
     strategy:
       fail-fast: false
@@ -238,6 +246,8 @@ jobs:
 
   # ICU4J performance test for Unicode sets
   icu4j-unicodesetperf:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     strategy:
       fail-fast: false
       matrix:
@@ -287,6 +297,8 @@ jobs:
 
   # ICU4J performance test for character APIs
   icu4j-ucharacterperf:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     strategy:
       fail-fast: false
 
@@ -333,6 +345,8 @@ jobs:
 
   # ICU4J performance test for decimal formatting
   icu4j-decimalformatperf:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     strategy:
       fail-fast: false
       matrix:
@@ -386,6 +400,8 @@ jobs:
 
   # ICU4J performance test for normalization
   icu4j-normperf:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     strategy:
       fail-fast: false
       matrix:
@@ -443,6 +459,8 @@ jobs:
 
   # ICU4J performance test for encoding conversion
   icu4j-converterperf:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     strategy:
       fail-fast: false
       matrix:
@@ -566,6 +584,8 @@ jobs:
 
   # ICU4J performance test for date formatting
   icu4j-dateformatperf:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     strategy:
       fail-fast: false
       matrix:
@@ -637,6 +657,8 @@ jobs:
 
   # Retrieve performance test results and upload results to remote repository
   perf-test-data-move:
+    # Run performance tests only on the main branch of the ICU repository.
+    if: github.repository == 'unicode-org/icu' && github.ref == 'refs/heads/main'
     name: Copy perf data to remote repo for visualization
     needs: [icu4c-performance-tests, icu4c-performance-tests-with-files, icu4c-strsrchperf, icu4j-unicodesetperf, icu4j-ucharacterperf, icu4j-decimalformatperf, icu4j-normperf, icu4j-converterperf, icu4j-dateformatperf]
     runs-on: ubuntu-latest