Clean up 8.x branch

[colleenmcginnis]

In #1799, some unintended changes were pulled in when the base branch from changed from main to 8.x. This PR:

• Reverts that commit
• Cherry-picks the relevant release note commit (d4ddbac)
• Cleans up the formatting of the release notes

cc @alexandra5000

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[karenzone]

LGTM