return type for valid regex

Author: liustve

contract-tests/tests/test/amazon/base/contract_test_base.py

@@ -239,7 +239,7 @@ def _assert_metric_attributes(
     ):
         self.fail("Tests must implement this function")
 
-    def _is_valid_regex(self, pattern: str):
+    def _is_valid_regex(self, pattern: str) -> bool:
         try:
             re.compile(pattern)
             return True