ENH: Allow plus signs in labels #31

Job	Run time
Build & verify package	29s
Push package to test.pypi.org	0s
test (ubuntu-latest, 3.9, full, repo)	2m 58s
test (ubuntu-latest, 3.10, full, repo)	2m 56s
test (ubuntu-latest, 3.11, full, repo)	2m 47s
test (ubuntu-latest, 3.11, pre, repo)	2m 57s
test (ubuntu-latest, 3.12, full, repo)	3m 56s
test (ubuntu-latest, 3.12, pre, repo)	3m 54s
test (ubuntu-latest, 3.13, full, repo)	3m 36s
test (ubuntu-latest, 3.13, pre, repo)	3m 34s
test (macos-latest, 3.9, full, repo)	2m 38s
test (macos-latest, 3.10, full, repo)	2m 5s
test (macos-latest, 3.11, full, repo)	2m 9s
test (macos-latest, 3.11, pre, repo)	2m 39s
test (macos-latest, 3.12, full, repo)	2m 3s
test (macos-latest, 3.12, pre, repo)	2m 36s
test (macos-latest, 3.13, full, repo)	2m 4s
test (macos-latest, 3.13, pre, repo)	2m 18s
test (ubuntu-latest, 3.9, min, repo)	3m 12s
test (ubuntu-latest, 3, full, sdist)	3m 10s
Publish released package to pypi.org	0s
	52m 1s

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