back to Xcode 15 for rtdb integration

Author: paulb777

.github/workflows/database.yml

@@ -42,7 +42,7 @@ jobs:
   integration:
     # 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-15
+    runs-on: macos-14
     steps:
     - uses: actions/checkout@v4
     - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126
@@ -53,6 +53,8 @@ jobs:
       run: scripts/setup_bundler.sh
     - name: Install xcpretty
       run: gem install xcpretty
+    - name: Xcode
+      run: sudo xcode-select -s /Applications/Xcode_15.2.app/Contents/Developer
     - name: IntegrationTest
       # Only iOS to mitigate flakes.
       run: scripts/third_party/travis/retry.sh scripts/build.sh Database iOS integration