Prepare PL 3.4.1 release

[sstopfer]

This issue is to track preparation of the upcoming 3.4.1 release up until publishing, which is due September 23, 2024.

• [x] Create release/3.4.1 branch closer to the release date
• [x] Finalize scope and punt unfinished pull requests to following release
• [x] Smoke test (Friday, September 20, 2024)
• [x] Prepare the release (Monday, September 23, 2024)

[westonruter]

I've downgraded the version bump from 3.5.0 to 3.4.1 since there are minimal changes in the PL plugin itself: https://github.com/WordPress/performance/milestone/70?closed=1

[mukeshpanchal27]

Everything looks good from what I can see for the smoke test for version 3.4.1 through the trunk branch.

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