warning or hint unused case _:

### Describe the Bug

```py
from enum import StrEnum, auto
class A(StrEnum):
AA = auto()
BB = auto()

def f(a: A):
match a:
case A.AA:
...
case A.BB:
...
case _:
...
```

### Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeSIAxAAQDqMUAxrgLYzUAuunAFuwAqkATjDBRS1AMoYcBADS8IcakuqpqxVAHMYAHXQ0A7nxHVSuAK7VGGaoaEQOMBXB6pTM6rHfo1eCxycpMQQ6FoqvoIcPLjohPqUCdQAEjAeHtaWxLDUYDCoHBYiyrhgispoWHj4iEkAtNQA4jCBIqhQdRwQbEHE7Ix8jADWoeF5MDiow-XUAKpw7CIAbvlQAPocwTAAFACUnNyhcH2MgaF5QiKYvfAzMPh9DmzogYaOPLzsAJIAIgCiuXyhWKvAKdnYcAsxGIuCEgW2MEIWkIagCuGYLGyLWc1C0uE6%2BMwolCjggsQUMRWQgULUYuxmtAcTjUWGoQgskVI0VimSJ1EwEBEp3EETMliE1GwQlwhgWQn0YGlLGoMHQFmV3RhcKkHCEfzVLAUqDR%2BkYUFQcGUAEFtpJdfr1btar5qK6rVbqABeVFcPb6V2ugBCga9PtwfvQ%2BiJZTA21QiGoVqd-oDLAKAzUzoD2esFvYVsI7qzOZLhDLKZLNgWicIweLJezZfiLsreeoa3rDddTf0vfQIDkIDIIjEpEIXBYUAoNEEI5FlVk%2BEy6EgWiKBTJcSSkhg7B4HA4xDgiAA9Cfh6JxIRYVoT6qT5h0XAT8wVxA10IN7ET7lYWolqg0CoNgOSvqu65dDyuDEJB6BwM2ZDcugdRUnAm6hroIAAMyEAAjAATJh%2BgANppNKQhwAAuvoHKarCTiYHUApCl0KyhgA5O%2B6CwjA7H6NxHB1CIACOFiChMdRDDApB1FMjDwMo3rsYYPh8f2AC%2Bg5TKxMAAGLQDAFALtUJDkOpQA

### (Only applicable for extension issues) IDE Information

_No response_