Add `accepted_user_id` to invitation #1297

Job	Run time
Test Python 3.10	22s
Test Python 3.11	22s
Test Python 3.8	25s
Test Python 3.12	26s
Test Python 3.9	21s
Test Python 3.14	42s
Test Python 3.13	21s
Smoke test (Python ${{ matrix.python }})	0s
	2m 59s

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