== override parameters are non-nullable (#2400)

* == override parameters are non-nullable

Make operator == override parameters no-nullable. See dart-lang/linter#3441

Work towards dart-lang/sdk#51038.

* Update fake_google_account.dart
diff --git a/dashboard/test/utils/fake_google_account.dart b/dashboard/test/utils/fake_google_account.dart
index 898f07a..fac20ea 100644
--- a/dashboard/test/utils/fake_google_account.dart
+++ b/dashboard/test/utils/fake_google_account.dart
@@ -31,8 +31,8 @@
   Future<void> clearAuthCache() => Future<void>.value(null);
 
   @override
-  bool operator ==(dynamic other) {
-    final GoogleSignInAccount otherAccount = other;
+  bool operator ==(Object other) {
+    final GoogleSignInAccount otherAccount = other as GoogleSignInAccount;
     return email == otherAccount.email;
   }