PEP 751: Fix typos

[groodt]

• 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)

[ghost]

All commit authors signed the Contributor License Agreement.

[Rosuav]

👍 Two easy typos, LGTM.

[hugovk]

I've pushed a few more typo fixes.

[brettcannon]

Thanks, everyone!