[skip ci] rename test class

Author: ncooke3

FirebaseAuth/Tests/Unit/AuthBackendRPCImplementationTests.swift renamed to FirebaseAuth/Tests/Unit/AuthBackendTests.swift

@@ -27,7 +27,7 @@ private let kFakeAPIKey = "kTestAPIKey"
 private let kFakeAppID = "kTestFirebaseAppID"
 
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
-class AuthBackendRPCImplementationTests: RPCBaseTests {
+class AuthBackendTests: RPCBaseTests {
   let kFakeErrorDomain = "fakeDomain"
   let kFakeErrorCode = -1