Update sphinx requirement from <8 to <9 #1293

Job	Run time
ensure-catalog-matches-hook-config	24s
Run tests on ubuntu-latest, py3.8	1m 33s
Run tests on ubuntu-latest, py3.9	1m 33s
Run 'mypy' on python 3.x	22s
Run tests on ubuntu-latest, py3.10	1m 27s
Run 'twine-check' on python 3.x	17s
Run tests on ubuntu-latest, py3.11	1m 24s
Run 'py-mindeps' on python 3.8	25s
Run tests on ubuntu-latest, py3.12	1m 41s
Run tests on windows-latest, py3.8	2m 30s
Self-Check	12s
Run tests on windows-latest, py3.9	2m 8s
Run tests on windows-latest, py3.10	2m 9s
Run tests on windows-latest, py3.11	2m 15s
test-sdist	1m 37s
Run tests on windows-latest, py3.12	2m 50s
Run tests on macos-latest, py3.8	1m 43s
Run tests on macos-latest, py3.9	1m 0s
Run tests on macos-latest, py3.10	1m 2s
Run tests on macos-latest, py3.11	1m 1s
Run tests on macos-latest, py3.12	1m 8s
Collate results to check for skipped tests	8s
	28m 49s

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