Fix validation of datetime-formatted strings #1559

Job	Run time
linux-gallery-python3.12-upgraded	58s
linux-gallery-python3.8-minimum	54s
windows-gallery-python3.12-upgraded	2m 1s
windows-gallery-python3.8-minimum	1m 34s
linux-gallery-python3.12-ros3	1m 33s
linux-python3.12	2m 15s
linux-python3.8-minimum	1m 58s
linux-python3.12-upgraded	2m 20s
macos-python3.12-upgraded	3m 23s
macos-python3.8-minimum	2m 35s
windows-python3.12-upgraded	3m 42s
windows-python3.8-minimum	3m 14s
conda-linux-python3.12-upgraded	2m 49s
conda-linux-python3.8-minimum	2m 34s
Deploy pre-release from dev	0s
	31m 50s

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