fix(ci): annotate cache.py:38 redis return type (CAR-1330 dev lint fix)

mypy no-any-return: annotate value: str | bytes | None so mypy doesn't
widen redis client return to Any. Pre-existing dev branch issue blocking
CAR-1356. Mirrors CAR-1340 uat fix (2b20946).

src/cartsnitch_api/cache.py

@@ -35,7 +35,7 @@ class CacheClient:
     async def get(self, key: str) -> str | None:
         if not self._client:
             return None
-        value = await self._client.get(key)
+        value: str | bytes | None = await self._client.get(key)
         if value is None:
             return None
         if isinstance(value, bytes):