Fixing enforce_metadata doc, not checking for dtypes

[epizut]

The current apply_and_enforce() implementation does not raise on mismatching dtypes so we need to update the doc accordingly

• Closes dask.dataframe.map_partitions enforce_metadata not checking for dtypes #9466
• Tests added / passed
• Passes pre-commit run --all-files

[GPUtester]

Can one of the admins verify this patch?

Admins can comment ok to test to allow this one PR to run or add to allowlist to allow all future PRs from the same author to run.

[phobson]

Thanks for the PR, @epizut. This looks good to me.

[jsignell]

I think the original intent of the docstrings was types (like DataFrame vs Series), not dtype but I'm fine with the change.

[epizut]

Makes sense,
Now, the docstring specifically says 'dtypes' so there is no ambiguity.

[ncclementi]

@epizut Thank you for this contribution, this goes in! Congrats on your first PR to dask 🎉