Use the same `now` for all in merge check #256

Job	Run time
Build distribution packages	22s
Test with nox (amd64, ubuntu-24.04, 3.12, ci_checks_max)	1m 43s
Test with nox (amd64, ubuntu-24.04, 3.12, pytest_min)	1m 11s
Test with nox (arm, ubuntu-24.04, 3.11, ci_checks_max)	1m 59s
Test with nox (arm, ubuntu-24.04, 3.12, ci_checks_max)	2m 0s
Test with nox (arm, ubuntu-24.04, 3.12, pytest_min)	1m 41s
Test with nox (amd64, ubuntu-24.04, 3.11, ci_checks_max)	1m 41s
Test with nox (arm, ubuntu-24.04, 3.11, pytest_min)	1m 38s
Test with nox (amd64, ubuntu-24.04, 3.11, pytest_min)	1m 4s
Test documentation website generation	0s
Test package installation (amd64, ubuntu-24.04, 3.11)	16s
Test package installation (arm, ubuntu-24.04, 3.12)	41s
Test package installation (arm, ubuntu-24.04, 3.11)	52s
Test package installation (amd64, ubuntu-24.04, 3.12)	23s
Test package installation	2s
Test with nox	2s
Publish documentation website to GitHub pages	31s
Create GitHub release	-1s
Publish packages to PyPI	0s
	16m 5s

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