Enable exhaustive-match in mypy (#11409)

Author: Dreamsorcerer

.mypy.ini

@@ -11,7 +11,7 @@ disallow_untyped_calls = True
 disallow_untyped_decorators = True
 disallow_untyped_defs = True
 # TODO(PY312): explicit-override
-enable_error_code = deprecated, ignore-without-code, possibly-undefined, redundant-expr, redundant-self, truthy-bool, truthy-iterable, unused-awaitable
+enable_error_code = deprecated, exhaustive-match, ignore-without-code, possibly-undefined, redundant-expr, redundant-self, truthy-bool, truthy-iterable, unused-awaitable
 extra_checks = True
 follow_untyped_imports = True
 implicit_reexport = False