PEP 612: Mark as Final

[hugovk]

• Final implementation has been merged (including tests and docs)
• PEP matches the final implementation
• Any substantial changes since the accepted version approved by the SC/PEP delegate
• Pull request title in appropriate format (PEP 123: Mark Final)
• Status changed to Final (and Python-Version is correct)
• Canonical docs/spec linked with a canonical-doc directive (or canonical-pypa-spec, for packaging PEPs)

Helps #2872 and #3579.

Link to https://docs.python.org/3/library/typing.html#typing.ParamSpec as the canonical docs, and remove a redundant header.

cc @Fidget-Spinner

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📚 Documentation preview 📚: https://pep-previews--3575.org.readthedocs.build/pep-0612/

[Fidget-Spinner]

Implementation is done. Jelle and I implemented it https://docs.python.org/3/whatsnew/3.10.html#pep-612-parameter-specification-variables.

[Fidget-Spinner]

Small comment

[JelleZijlstra]

Thanks!