Update sphinx-rtd-theme to 3.0.0 #1783

Job	Run time
Build and test (ubuntu-latest, 3.8)	17s
Build and test (ubuntu-latest, 3.9)	14s
Build and test (ubuntu-latest, 3.10)	13s
Build and test (ubuntu-latest, 3.11)	13s
Build and test (ubuntu-latest, 3.12)	17s
Build and test (ubuntu-latest, 3.13-dev)	1m 12s
Build and test (windows-latest, 3.8)	1m 2s
Build and test (windows-latest, 3.9)	52s
Build and test (windows-latest, 3.10)	1m 5s
Build and test (windows-latest, 3.11)	43s
Build and test (windows-latest, 3.12)	1m 21s
Build and test (windows-latest, 3.13-dev)	1m 50s
Build and test (macos-latest, 3.8)	41s
Build and test (macos-latest, 3.9)	19s
Build and test (macos-latest, 3.10)	18s
Build and test (macos-latest, 3.11)	25s
Build and test (macos-latest, 3.12)	21s
Build and test (macos-latest, 3.13-dev)	1m 10s
	12m 33s

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