DOC: update sphinx to latest version (#104) #520

Job	Run time
lint (ubuntu-latest, 3.10)	46s
build_test_job (ubuntu-latest, 3.8, xoscar)	6m 12s
build_test_job (ubuntu-latest, 3.9, xoscar)	5m 54s
build_test_job (ubuntu-latest, 3.10, xoscar)	6m 1s
build_test_job (ubuntu-latest, 3.11, xoscar)	5m 48s
build_test_job (macos-13, 3.8, xoscar)	8m 44s
build_test_job (macos-13, 3.11, xoscar)	8m 52s
build_test_job (windows-latest, 3.8, xoscar)	12m 4s
build_test_job (windows-latest, 3.11, xoscar)	9m 39s
build_test_job (self-hosted, gpu, 3.11)	4m 32s
build_test_job (ubuntu-20.04, doc-build, 3.9)	4m 7s
	1h 12m 39s

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