textproc/py-pymdown-extensions: Update to 9.9.2

• Switch to PEP517 build framework and remove no longer required setuptools workaround.

Changelog since 9.9:

https://github.com/facelessuser/pymdown-extensions/compare/9.9...9.9.2

MFH: No (PEP517 support not present in 2023Q1 branch)