## Summary
Given `key in obj.keys()`, `obj` _could_ be a dictionary, or it could be
another type that defines
a `.keys()` method. In the latter case, removing the `.keys()` attribute
could lead to a runtime error.
Previously, we marked all `SIM118` fixes as unsafe for this reason;
however, in preview, we now mark them as safe if we can
infer that the expression is a dictionary.
## Test Plan
Added a preview fixture.
37301375c8