[Infra] Update firestore.yml

Author: ncooke3

.github/workflows/firestore.yml

@@ -572,7 +572,7 @@ jobs:
   spm-binary-cron:
     # Don't run on private repo.
     if: github.event_name == 'schedule' && github.repository == 'Firebase/firebase-ios-sdk'
-    runs-on: macos-14
+    runs-on: macos-15
     strategy:
       matrix:
         target: [tvOS, macOS, catalyst]
@@ -581,6 +581,8 @@ jobs:
     - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126
       with:
         cache_key: ${{ matrix.target }}
+    - name: Xcode
+      run: sudo xcode-select -s /Applications/Xcode_16.2.app/Contents/Developer
     - name: Initialize xcodebuild
       run: scripts/setup_spm_tests.sh
     - name: Build Test - Binary