correct my accidental omittion of a negation

Author: wyattscarpenter

mypy/errors.py

@@ -630,7 +630,7 @@ def add_error_info(self, info: ErrorInfo) -> None:
             self.only_once_messages.add(info.message)
         if (
             self.seen_import_error
-            and ErrorCode.is_code_or_sub_code_of(info.code, IMPORT)
+            and not ErrorCode.is_code_or_sub_code_of(info.code, IMPORT)
             and self.has_many_errors()
         ):
             # Missing stubs can easily cause thousands of errors about