firebase13: bump minimum macOS to 11.0 and watchOS to 8.0 (#16551)

FirebaseFunctions.podspec

@@ -19,9 +19,9 @@ Cloud Functions for Firebase.
   s.swift_version    = '5.9'
 
   ios_deployment_target = '15.0'
-  osx_deployment_target = '10.15'
+  osx_deployment_target = '11.0'
   tvos_deployment_target = '15.0'
-  watchos_deployment_target = '7.0'
+  watchos_deployment_target = '8.0'
 
   s.ios.deployment_target = ios_deployment_target
   s.osx.deployment_target = osx_deployment_target
@@ -46,7 +46,7 @@ Cloud Functions for Firebase.
   s.test_spec 'objc' do |objc_tests|
     objc_tests.platforms = {
       :ios => ios_deployment_target,
-      :osx => '10.15',
+      :osx => osx_deployment_target,
       :tvos => tvos_deployment_target
     }
     objc_tests.source_files = [