fix: manually install watchOS sims for messaging watch app (#15605)

Author: ncooke3

.github/workflows/messaging.yml

@@ -198,6 +198,8 @@ jobs:
       run: scripts/install_prereqs.sh MessagingSampleStandaloneWatchApp watchOS
     - name: Xcode
       run: sudo xcode-select -s /Applications/Xcode_16.4.app/Contents/Developer
+    - name: Install watchOS simulators in case they are missing.
+      run: sudo xcodebuild -downloadPlatform watchOS
     - name: Build
       run: ([ -z $plist_secret ] || scripts/build.sh MessagingSampleStandaloneWatchApp watchOS)
     - name: Upload xcodebuild logs