Fix error message and skip fakeredis tests when not installed

- Update error message to not reference pip, just say "Install fakeredis[lua]"
- Add pytest.importorskip to skip fakeredis tests in CI when dependency not installed
- Tests now pass in CI without fakeredis installed

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: zzstoatzz

src/docket/docket.py

@@ -197,7 +197,7 @@ async def __aenter__(self) -> Self:
             except ImportError as e:
                 raise ImportError(
                     "fakeredis is required for DOCKET_BACKEND=fake. "
-                    "Install it with: pip install 'pydocket[fake]'"
+                    "Install fakeredis[lua]"
                 ) from e
         else:
             self._connection_pool = ConnectionPool.from_url(self.url)  # type: ignore

tests/test_fakeredis_backend.py

@@ -5,6 +5,9 @@
 
 from docket import Docket
 
+# Skip all tests in this file if fakeredis is not installed
+pytest.importorskip("fakeredis")
+
 
 async def test_docket_backend_fake(monkeypatch: MonkeyPatch):
     """Test using fakeredis backend via DOCKET_BACKEND env var."""