Add back fix for g3 warnings (#8645)

Author: ncooke3

Functions/Example/Tests/FIRFunctionsTests.m

@@ -161,8 +161,11 @@ - (void)testCallFunctionWhenAppCheckIsInstalledAndFACTokenSuccess {
 
   XCTestExpectation *httpRequestExpectation =
       [self expectationWithDescription:@"HTTPRequestExpectation"];
+  __weak __auto_type weakSelf = self;
   _fetcherService.testBlock = ^(GTMSessionFetcher *_Nonnull fetcherToTest,
                                 GTMSessionFetcherTestResponse _Nonnull testResponse) {
+    // __unused to avoid warning in Xcode 12+ in g3.
+    __unused __auto_type self = weakSelf;
     [httpRequestExpectation fulfill];
 
     NSString *appCheckTokenHeader =
@@ -225,9 +228,11 @@ - (void)testCallFunctionWhenAppCheckIsNotInstalled {
 
   XCTestExpectation *httpRequestExpectation =
       [self expectationWithDescription:@"HTTPRequestExpectation"];
-
+  __weak __auto_type weakSelf = self;
   _fetcherService.testBlock = ^(GTMSessionFetcher *_Nonnull fetcherToTest,
                                 GTMSessionFetcherTestResponse _Nonnull testResponse) {
+    // __unused to avoid warning in Xcode 12+ in g3.
+    __unused __auto_type self = weakSelf;
     [httpRequestExpectation fulfill];
 
     NSString *appCheckTokenHeader =