support boolean variables also with the bool type keyword #28

Job	Run time
ci / container	1m 2s
ci / build-ui	43s
ci / docs	1m 0s
ci / Verify dev env (ubuntu-latest)	16s
ci / Verify dev env (macos-latest)	28s
ci / Verify dev env (windows-latest)	42s
ci / Linting	38s
ci / Build & verify package	24s
ci / tests on Python 3.11 / Gitlab 16.3.3-ce.0	7m 11s
ci / Typing	1m 7s
deploy-pypi	47s
deploy-ghcr	1m 25s
	15m 43s

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