Fix installation of extras with underscore #105

Job	Run time
test 3.13 on ubuntu-latest	4m 24s
tox env type on ubuntu-latest	50s
test 3.13 on windows-latest	14m 28s
tox env type on windows-latest	1m 59s
test 3.13 on macos-latest	5m 18s
tox env dev on ubuntu-latest	32s
tox env dev on windows-latest	1m 25s
test 3.12 on ubuntu-latest	4m 39s
tox env docs on ubuntu-latest	4m 32s
test 3.12 on windows-latest	14m 39s
tox env pkg_meta on ubuntu-latest	19s
test 3.12 on macos-latest	6m 34s
tox env pkg_meta on windows-latest	49s
test 3.11 on ubuntu-latest	3m 46s
test 3.11 on windows-latest	13m 34s
test 3.11 on macos-latest	4m 20s
test 3.10 on ubuntu-latest	3m 33s
test 3.10 on windows-latest	11m 15s
test 3.10 on macos-latest	4m 34s
test 3.9 on ubuntu-latest	3m 40s
test 3.9 on windows-latest	10m 13s
test 3.9 on macos-latest	4m 27s
test 3.8 on ubuntu-latest	3m 38s
test 3.8 on windows-latest	12m 55s
test 3.8 on macos-latest	4m 32s
	2h 20m 55s

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