Messaging: fix a warning in macOS build and sample podfile file path (#6070)

Example/watchOSSample/Podfile

@@ -3,19 +3,19 @@ use_frameworks!
 target 'SampleWatchAppWatchKitExtension' do
   platform :watchos, '6.0'
 
-  pod 'FirebaseCore', :path => '../../../../../'
-  pod 'GoogleUtilities', :path => '../../../../../'
-  pod 'FirebaseMessaging', :path => '../../../../../'
-  pod 'FirebaseInstanceID', :path => '../../../../../'
-  pod 'FirebaseCoreDiagnostics', :path => '../../../../../'
-  pod 'GoogleDataTransport', :path => '../../../../../'
-  pod 'FirebaseInstallations', :path => '../../../../../'
-  pod 'FirebaseStorage', :path => '../../../../../'
+  pod 'FirebaseCore', :path => '../../'
+  pod 'GoogleUtilities', :path => '../../'
+  pod 'FirebaseMessaging', :path => '../../'
+  pod 'FirebaseInstanceID', :path => '../../'
+  pod 'FirebaseCoreDiagnostics', :path => '../../'
+  pod 'GoogleDataTransport', :path => '../../'
+  pod 'FirebaseInstallations', :path => '../../'
+  pod 'FirebaseStorage', :path => '../../'
 
 end
 
 target 'ServiceExtension' do
   platform :watchos, '6.0'
-  pod 'FirebaseMessaging', :path => '../../../../../'
-  pod 'FirebaseInstanceID', :path => '../../../../../'
+  pod 'FirebaseMessaging', :path => '../../'
+  pod 'FirebaseInstanceID', :path => '../../'
 end

FirebaseMessaging/Tests/UnitTests/FIRMessagingContextManagerServiceTest.m

@@ -31,6 +31,7 @@ static NSString *const kUserInfoValue2 = @"Yes";
 static NSString *const kMessageIdentifierKey = @"gcm.message_id";
 static NSString *const kMessageIdentifierValue = @"1584748495200141";
 
+API_AVAILABLE(macos(10.14))
 @interface FIRMessagingContextManagerServiceTest : XCTestCase
 
 @property(nonatomic, readwrite, strong) NSDateFormatter *dateFormatter;