Remove need to use `tempfile` #90

Job	Run time
validation (ubuntu-latest, stable)	30s
validation (ubuntu-latest, beta)	34s
validation (macos-latest, stable)	1m 12s
validation (macos-latest, beta)	1m 18s
validation (windows-latest, stable)	2m 10s
validation (windows-latest, beta)	1m 14s
	6m 58s

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