Do not emit redundant-expr warnings for if TYPE_CHECKING statements.

Author: tyralla

mypy/checker.py

@@ -5019,7 +5019,10 @@ def visit_if_stmt(self, s: IfStmt) -> None:
 
                 if_map, else_map = self.find_isinstance_check(e)
 
-                if codes.REDUNDANT_EXPR in self.options.enabled_error_codes:
+                if codes.REDUNDANT_EXPR in self.options.enabled_error_codes and not (
+                    isinstance(e, NameExpr)
+                    and e.fullname in ("typing.TYPE_CHECKING", "typing_extensions.TYPE_CHECKING")
+                ):
                     if if_map is None:
                         if s.while_stmt:
                             self.msg.redundant_condition_in_while(e)