[3.12] pythonGH-109190: Copyedit 3.12 What's New: Release highlights (pythonGH-109770) (python#109971)

* pythonGH-109190: Copyedit 3.12 What's New: Release highlights (pythonGH-109770)
(cherry picked from commit b35f084)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

* Delete bad merge leftovers

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Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Author: miss-islington