[ci][desktop] add appstream check

Signed-off-by: Francesco Gazzetta <fgaz@fgaz.me>

.github/workflows/linux-check.yaml

@@ -148,3 +148,26 @@ jobs:
             -e routing_consistency_tests \
             -e opening_hours_supported_features_tests \
             -e storage_integration_tests \
+
+  linux-appstream:
+    name: Linux validate appstream data
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install appstream validator
+        shell: bash
+        run: |
+          sudo apt update -y
+          sudo apt install -y \
+              flatpak
+          sudo flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
+          # We get it from flathub to ensure we have a recent version
+          sudo flatpak install -y org.freedesktop.appstream-glib
+
+      - name: Validate appstream data
+        shell: bash
+        run: flatpak run org.freedesktop.appstream-glib validate --nonet qt/res/app.organicmaps.desktop.metainfo.xml