[python+docs]: Update sphinx-rtd-theme requirement in /docs #871

Job	Run time
test-install-vcs (macos-latest, 3.7)	19s
test-install-vcs (macos-latest, 3.8)	20s
test-install-vcs (macos-latest, 3.9)	34s
test-install-vcs (macos-latest, 3.10)	23s
test-install-vcs (macos-latest, 3.11)	21s
test-install-vcs (macos-latest, 3.12)	24s
test-install-vcs (macos-latest, pypy-3.7)	31s
test-install-vcs (macos-latest, pypy-3.8)	32s
test-install-vcs (macos-latest, pypy-3.9)	24s
test-install-vcs (macos-latest, pypy-3.10)	24s
test-install-vcs (ubuntu-latest, 3.7)	13s
test-install-vcs (ubuntu-latest, 3.8)	11s
test-install-vcs (ubuntu-latest, 3.9)	14s
test-install-vcs (ubuntu-latest, 3.10)	13s
test-install-vcs (ubuntu-latest, 3.11)	11s
test-install-vcs (ubuntu-latest, 3.12)	11s
test-install-vcs (ubuntu-latest, pypy-3.7)	29s
test-install-vcs (ubuntu-latest, pypy-3.8)	25s
test-install-vcs (ubuntu-latest, pypy-3.9)	24s
test-install-vcs (ubuntu-latest, pypy-3.10)	24s
test-install-vcs (windows-latest, 3.7)	42s
test-install-vcs (windows-latest, 3.8)	43s
test-install-vcs (windows-latest, 3.9)	40s
test-install-vcs (windows-latest, 3.10)	29s
test-install-vcs (windows-latest, 3.11)	33s
test-install-vcs (windows-latest, 3.12)	33s
test-install-vcs (windows-latest, pypy-3.7)	1m 9s
test-install-vcs (windows-latest, pypy-3.8)	1m 5s
test-install-vcs (windows-latest, pypy-3.9)	1m 2s
test-install-vcs (windows-latest, pypy-3.10)	1m 31s
	15m 34s

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