Revert "containers: Cap sphinx at 7 to unblock CI." #202

Job	Run time
Prepare container	3m 18s
linux rpm fedora	6m 52s
osx clang --disable-ssl	2m 10s
linux gcc --disable-ssl	2m 37s
linux clang --disable-ssl	2m 39s
linux gcc test -300	9m 18s
linux gcc test 301-600	6m 5s
linux gcc test 601- unstable	6m 42s
linux clang test sanitizers -300	12m 28s
linux clang test sanitizers 301-600	8m 39s
linux clang test sanitizers 601- unstable	10m 50s
linux gcc test -ljemalloc -300	9m 32s
linux gcc test -ljemalloc 301-600	6m 28s
linux gcc test -ljemalloc 601- unstable	6m 40s
linux gcc system-test-dpdk dpdk -100	17m 15s
linux gcc system-test-dpdk dpdk 101- unstable	12m 12s
linux gcc system-test-userspace -100	15m 31s
linux gcc system-test-userspace 101- unstable	10m 59s
linux gcc system-test -100	18m 10s
linux gcc system-test 101- unstable	14m 33s
linux clang system-test sanitizers -100	19m 59s
linux clang system-test sanitizers 101- unstable	16m 16s
linux x86 gcc --disable-ssl	2m 50s
	3h 42m 3s

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