Update timed integration tests to run on macos-15 (#14698)

Author: paulb777

.github/workflows/performance-integration-tests.yml

@@ -27,7 +27,7 @@ jobs:
     if: github.repository == 'Firebase/firebase-ios-sdk'
     env:
       plist_secret: ${{ secrets.GHASecretsGPGPassphrase1 }}
-    runs-on: macos-14
+    runs-on: macos-15
     steps:
     - uses: actions/checkout@v4
     - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126

.github/workflows/sessions-integration-tests.yml

@@ -27,9 +27,11 @@ jobs:
     if: github.repository == 'Firebase/firebase-ios-sdk'
     env:
       plist_secret: ${{ secrets.GHASecretsGPGPassphrase1 }}
-    runs-on: macos-14
+    runs-on: macos-15
     steps:
     - uses: actions/checkout@v4
+    - name: Xcode
+      run: sudo xcode-select -s /Applications/Xcode_16.2.app/Contents/Developer
     - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126
       with:
         cache_key: sessions-integration-tests