Restore GHA matrix with SPM cache

Author: paulb777

.github/workflows/spm.yml

@@ -23,6 +23,25 @@ jobs:
         if: ${{ github.event_name == 'schedule' }}
         run: echo '::set-output name=WAS_CHANGED::'$(test -n "$(git log --format=%H --since='24 hours ago')" && echo 'true' || echo 'false')
 
+
+  spm-package-resolved:
+    runs-on: macos-14
+    outputs:
+      package_resolved_hash: ${{ steps.cache.outputs.cache-primary-key }}
+    env:
+      FIREBASECI_USE_LATEST_GOOGLEAPPMEASUREMENT: 1
+    steps:
+      - uses: actions/checkout@v4
+      - name: Generate Swift Package.resolved
+        id: swift_package_resolve
+        run: |
+          swift package resolve
+      - uses: actions/cache/save@v4
+        id: cache
+        with:
+          path: .build
+          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
+
   spm:
     needs: changed_today
     if: ${{ github.event_name == 'pull_request' || needs.changed_today.outputs.WAS_CHANGED == 'true' }}
@@ -31,13 +50,18 @@ jobs:
       matrix:
         os: [macos-14]
         target: [iOS, tvOS, macOS, catalyst, visionOS]
-        xcode: [Xcode_15.2, Xcode_15.4, Xcode_16_Release_Candidate]
+        xcode: [Xcode_15.2, Xcode_15.4, Xcode_16]
     runs-on: ${{ matrix.os }}
+    needs: spm-package-resolved
     env:
       FIREBASE_MAIN: 1
       DISABLE_INTEGRATION_TESTS: 1
     steps:
     - uses: actions/checkout@v4
+    - uses: actions/cache/restore@v4
+      with:
+        path: .build
+        key: ${{ runner.os }}-spm-${{needs.spm-package-resolved.outputs.package_resolved_hash}}
     - name: Xcode
       run: sudo xcode-select -s /Applications/${{ matrix.xcode }}.app/Contents/Developer
     - name: Setup Scripts Directory