Fix usage of PlainSerializer with builtin types

[Viicos]

Change Summary

Related issue number

Fixes #9447

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist
• Tests pass on CI
• Documentation reflects the changes where applicable
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @alexmojaki

[Viicos]

@sydney-runkle, I believe you meant to use the function (well in this case the type) here in your previous fix?

[sydney-runkle]

Great, thanks!

[codspeed-hq]

CodSpeed Performance Report

Merging #9450 will not alter performance

_{Comparing Viicos:issue/plain-serializers (01a7c5e) with main (7bdfac3)}

Summary

✅ 13 untouched benchmarks

[Viicos]

Please review

[sydney-runkle]

Wonderful, thanks!

[sydney-runkle]

@Viicos, looks like some tests are failing?

[Viicos]

@sydney-runkle On PyPy, inspect.signature is able to get the signature of str:

<Signature (object=<no value>, encoding=<no value>, errors=<no value>)>

As the _serializer_info_arg function does not really take into account arguments with default values, it fails to determine if the info argument is required. I'll open a new issue with a clear example, in the meanwhile I disabled the test on PyPy so that this one can be merged.