PEP 798: Fixes and Clarifications from Discourse Thread

[adqm]

This PR represents a few small wording changes for PEP 798 (primarily in the "How to Teach This" section) based on discussion from the Discourse thread, attempting to fix some correctness issues and to clarify some points. It also fixes syntax highlighting for the examples from other languages.

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

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📚 Documentation preview 📚: https://pep-previews--4518.org.readthedocs.build/

[adqm]

@JelleZijlstra, just a heads-up there are likely more changes to be made here (I haven't yet made any changes to address the concerns about regular versus async generators from the Discourse thread, for example, other than adding a link to PEP 525).