Remove hard-coded version from pyproject.toml #31

Job	Run time
tests / Load tox environments	12s
tests / py39-test-psutil56 (ubuntu-latest)	43s
tests / py310-test-psutil57 (ubuntu-latest)	41s
tests / py311-test-psutil58-alldeps (ubuntu-latest)	58s
tests / py312-test-psutil59 (ubuntu-latest)	49s
tests / py39-test-psutil56 (macos-12)	1m 6s
tests / py310-test-psutil57 (macos-latest)	1m 4s
tests / py311-test-psutil58-alldeps (macos-latest)	1m 1s
tests / py312-test-psutil59 (macos-latest)	56s
tests / py39-test-psutil56 (windows-latest)	1m 47s
tests / py310-test-psutil57 (windows-latest)	2m 2s
tests / py311-test-psutil58-alldeps (windows-latest)	2m 26s
tests / py312-test-psutil59 (windows-latest)	1m 43s
publish / Build source and wheel distribution	1m 30s
	16m 58s

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