Fix ValueError crash when tab-set contains non-tab-item children #682

Job	Run time
pre-commit	15s
docs-build-format (man)	13s
docs-build-format (latex)	16s
docs-build-format (html)	13s
Tests (py3.12, Sphinx~=7.0, on ubuntu-latest)	47s
Tests (py3.11, Sphinx~=8.0, on ubuntu-latest)	34s
Tests (py3.11, Sphinx~=9.0, on ubuntu-latest)	38s
Tests (py3.14, Sphinx~=9.0, on ubuntu-latest)	27s
Tests (py3.14, Sphinx~=7.0, on ubuntu-latest)	35s
Tests (py3.13, Sphinx~=7.0, on ubuntu-latest)	45s
Tests (py3.12, Sphinx~=8.0, on ubuntu-latest)	40s
Tests (py3.12, Sphinx~=9.0, on ubuntu-latest)	42s
Tests (py3.11, Sphinx~=7.0, on windows-latest)	1m 16s
Tests (py3.13, Sphinx~=8.0, on ubuntu-latest)	36s
Tests (py3.14, Sphinx~=8.0, on ubuntu-latest)	29s
Tests (py3.11, Sphinx~=7.0, on ubuntu-latest)	42s
Tests (py3.13, Sphinx~=9.0, on ubuntu-latest)	36s
Tests (py3.13, Sphinx~=8.0, on windows-latest)	1m 22s
Tests (py3.14, Sphinx~=9.0, on windows-latest)	1m 6s
check	4s
Publish to PyPi	-1s
	12m 15s

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