[Infra] Migrate away from macos-12 in sessions-integration-tests.yml (#14130)

Author: ncooke3

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

@@ -26,8 +26,7 @@ jobs:
     if: github.repository == 'Firebase/firebase-ios-sdk'
     env:
       plist_secret: ${{ secrets.GHASecretsGPGPassphrase1 }}
-    #TODO(#12771): Fix macos-14 build issues
-    runs-on: macos-12
+    runs-on: macos-14
     steps:
     - uses: actions/checkout@v4
     - uses: mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126