requirements: update sphinx requirement from <4.2.1 to <8.0.3 #9196

Job	Run time
build (3.7, x64, ubuntu)	48m 19s
build (3.7, x64, windows)	50m 5s
build (3.11, x64, ubuntu)	1h 13m 13s
build (3.11, x64, macos)	28m 2s
build (3.11, x64, windows)	1h 16m 44s
build (3.12, x64, ubuntu)	1h 18m 42s
build (3.12, x64, macos)	25m 36s
build (3.12, x64, windows)	1h 14m 58s
build (3.9, macos, --cov=psyneulink)	36m 18s
build (3.9, ubuntu, --forked -m "not llvm")	32m 53s
build (3.8, x86, windows)	1h 21m 13s
build (3.10, ubuntu, --fp-precision=fp32)	1h 14m 54s
build (3.10, macos, -m benchmark --benchmark-enable --benchmark-only --benchmark-min-rounds=2 --b...	22m 48s
build (3.7, x64, ubuntu, min)	48m 0s
build (3.8, macos)	28m 27s
	13h 0m 12s

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