[Infra] Move 'client_app' workflow to Xcode 16 (#14684)

Author: ncooke3

.github/workflows/client_app.yml

@@ -25,19 +25,20 @@ concurrency:
 jobs:
   client-app-spm:
     if: (github.repository == 'Firebase/firebase-ios-sdk' && github.event_name == 'schedule') || github.event_name == 'pull_request'
-    runs-on: macos-14
     strategy:
       matrix:
         #TODO(ncooke3): Add multi-platform support: tvOS, macOS, catalyst
         platform: [iOS]
         scheme: [ClientApp]
+        os: [macos-14, macos-15]
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
       - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126
         with:
           cache_key: ${{ matrix.os }}
       - name: Xcode
-        run: sudo xcode-select -s /Applications/Xcode_15.2.app/Contents/Developer
+        run: sudo xcode-select -s /Applications/Xcode_16.2.app/Contents/Developer
       - name: Build Client App –– ${{ matrix.platform }}
         run: scripts/third_party/travis/retry.sh ./scripts/build.sh ${{ matrix.scheme }} ${{ matrix.platform }} xcodebuild
 
@@ -46,29 +47,31 @@ jobs:
       env:
         FIREBASECI_USE_LATEST_GOOGLEAPPMEASUREMENT: 1
         FIREBASE_SOURCE_FIRESTORE: 1
-      runs-on: macos-14
       strategy:
         matrix:
           #TODO(ncooke3): Add multi-platform support: tvOS, macOS, catalyst
           platform: [iOS]
           scheme: [ClientApp]
+          os: [macos-14, macos-15]
+      runs-on: ${{ matrix.os }}
       steps:
         - uses: actions/checkout@v4
         - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126
           with:
             cache_key: ${{ matrix.os }}
         - name: Xcode
-          run: sudo xcode-select -s /Applications/Xcode_15.2.app/Contents/Developer
+          run: sudo xcode-select -s /Applications/Xcode_16.2.app/Contents/Developer
         - name: Build Client App –– ${{ matrix.platform }}
           run: scripts/third_party/travis/retry.sh ./scripts/build.sh ${{ matrix.scheme }} ${{ matrix.platform }} xcodebuild
 
   client-app-cocoapods:
     # Don't run on private repo unless it is a PR.
     if: (github.repository == 'Firebase/firebase-ios-sdk' && github.event_name == 'schedule') || github.event_name == 'pull_request'
-    runs-on: macos-14
     strategy:
       matrix:
         scheme: [ClientApp-CocoaPods]
+        os: [macos-14, macos-15]
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
       - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126
@@ -78,7 +81,7 @@ jobs:
       - name: Setup Bundler
         run: scripts/setup_bundler.sh
       - name: Xcode
-        run: sudo xcode-select -s /Applications/Xcode_15.2.app/Contents/Developer
+        run: sudo xcode-select -s /Applications/Xcode_16.2.app/Contents/Developer
       - name: Prereqs
         run: scripts/install_prereqs.sh ClientApp iOS xcodebuild
       - name: Build