[PyYAML] Use Incomplete instead of Any

[donbarbos]

In some places, Any was intended to represent a Python object corresponding to a YAML value.
I think we could be more precise than simply using Any here for example, by defining a TypeAlias for the possible types (list, dict, etc.) and adding a comment explaining the choice.

[srittau]

In some places, Any was intended to represent a Python object corresponding to a YAML value.
I think we could be more precise than simply using Any here for example, by defining a TypeAlias for the possible types (list, dict, etc.) and adding a comment explaining the choice.

In general a type alias would also double as documentation and would make the comment for Any superfluous. But we probably need to distinguish between output types (= Any) and input types (= X | Y) for the usual union in output types problem.

[donbarbos]

Since any object can be passed as input (to 'dump' functions), I used the same type alias for it as well. It looks like we do need to use Any for both input and output types after all, just for different reasons.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

operator (https://github.com/canonical/operator)
- ops/storage.py:361: error: Unused "type: ignore" comment  [unused-ignore]

schemathesis (https://github.com/schemathesis/schemathesis)
+ src/schemathesis/core/deserialization.py:149: error: Unused "type: ignore" comment  [unused-ignore]
+ src/schemathesis/core/deserialization.py:157: error: Unused "type: ignore" comment  [unused-ignore]