Fix typing extensions

[matteius]

This addresses two things:

1.) Removes the duplicate of typing_extensions
2.) Ensures our version of it is on the PATH for pydantic.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix.rst, .feature.rst, .behavior.rst, .doc.rst. .vendor.rst. or .trivial.rst (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.