PEP 508: fix mistakes in the complete parsley grammar

[sify21]

trafficstars

fix mistakes in the parsley grammar

• Change is either:
  • [ ] To a Draft PEP
  • [ ] To an Accepted or Final PEP, with Steering Council approval
  • [x] To fix an editorial issue (markup, typo, link, header, etc)
• [x] PR title prefixed with PEP number (e.g. PEP 123: Summary of changes)

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:books: Documentation preview :books:: https://pep-previews--3070.org.readthedocs.build/

[cpython-cla-bot[bot]]

All commit authors signed the Contributor License Agreement.

[CAM-Gerlach]

(N.B., the button can be confusing, but you generally don't need to merge with main unless the CIs break, there's a merge conflict or you have another specific reason)

[arhadthedev]

@dstufft Can you review and possibly merge this PR, please?