fix string_format sanity check (#51780)

* newer version of Pylint moved the impl; use conditional import to find for new/old

(cherry picked from commit 6654c7aeea)

test/sanity/pylint/plugins/string_format.py

@@ -13,6 +13,9 @@ from pylint.interfaces import IAstroidChecker
 from pylint.checkers import BaseChecker
 from pylint.checkers import utils
 from pylint.checkers.utils import check_messages
+try:
+    from pylint.checkers.utils import parse_format_method_string
+except ImportError:
     from pylint.checkers.strings import parse_format_method_string
 
 _PY3K = sys.version_info[:2] >= (3, 0)