Derive the build ID's arch from the target archs

.github/workflows/build.yaml

@@ -213,6 +213,7 @@ jobs:
         path: aqtinstall.log
         if-no-files-found: error
     - name: Choose target architectures
+      id: arch
       run: |
         # Qt Online Installer only provides x86-64 binaries (not arm64) prior to Qt 6.2.0.
         if [[ '${{ matrix.qt }}' =~ ^(5|6\.[01])\. ]]; then arch=x86_64
@@ -222,13 +223,14 @@ jobs:
           if [[ '${{ matrix.os }}' == 'macos-13' ]]; then arx='x86_64'; else arch='arm64'; fi
         # Otherwise, default to universal binaries, where possible.
         else arch='arm64;x86_64'; fi
-        echo "CMAKE_OSX_ARCHITECTURES=${arch}" >> $GITHUB_ENV
+        echo "CMAKE_OSX_ARCHITECTURES=${arch}" | tee -a "$GITHUB_ENV"
+        echo "buildId=${arch//;/-}" | tee -a "$GITHUB_OUTPUT"
     - name: Build
       id: build
       env:
         CC:  ${{ matrix.env.cc }}
         CXX: ${{ matrix.env.cxx }}
-        PROJECT_BUILD_ID: ${{ github.run_number }}.${{ matrix.os }}.${{ startsWith(matrix.qt, '6') && 'arm64-' || '' }}x86_64.${{ matrix.env.cc }}${{ matrix.env.coverage && '-cov' || '' }}.qt-${{ matrix.qt }}
+        PROJECT_BUILD_ID: ${{ github.run_number }}.${{ matrix.os }}.${{ steps.arch.output.buildId }}.${{ matrix.env.cc }}${{ matrix.env.coverage && '-cov' || '' }}.qt-${{ matrix.qt }}
       run: |
         cmake -D CMAKE_BUILD_TYPE=Release \
               -D CODECOV_GCOV=${{ startsWith(matrix.env.cc, 'gcc') && '/usr/local/bin/gcov-12' || '/usr/bin/gcov'}} \