Use `py_require()` #412

Job	Run time
ubuntu-latest, tf-default, R-release	6m 52s
windows-latest, tf-default, R-release	6m 57s
macOS-latest, tf-default, R-release	3m 28s
windows-latest, tf-default, R-oldrel	10m 42s
macOS-latest, tf-default, R-oldrel	2m 43s
ubuntu-latest, tf-default, R-oldrel	4m 33s
ubuntu-latest, tf-default, R-oldrel-1	6m 6s
ubuntu-latest, tf-default, R-oldrel-2	7m 54s
ubuntu-latest, tf-default, R-oldrel-3	5m 0s
ubuntu-latest, tf-2.17, R-release	5m 49s
ubuntu-latest, tf-2.16, R-release	7m 19s
ubuntu-latest, tf-2.15, R-release	4m 49s
ubuntu-latest, tf-2.14, R-release	4m 46s
ubuntu-latest, tf-2.13, R-release	4m 53s
ubuntu-latest, tf-2.12, R-release	6m 45s
	1h 28m 36s

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