docs: Update Sphinx and myst-parser versions; resolve warnings #7351

Job	Run time
Documentation	3m 6s
Tests that may fail due to network or HTML	4m 7s
Long tests on Python 3.10	11m 36s
Linux tests (3.8)	8m 54s
Linux tests (3.9)	8m 43s
Linux tests (3.11)	7m 22s
Linux tests (3.12)	8m 16s
Windows long tests	1h 25m 46s
	2h 17m 50s

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