Run some workflows only on a weekly basis #554

Job	Run time
R-CMD-check / macOS-latest (release)	11m 4s
R-CMD-check / windows-latest (devel)	20m 2s
R-CMD-check / windows-latest (release)	24m 32s
R-CMD-check / windows-latest (oldrel)	27m 27s
R-CMD-check / ubuntu-latest (devel)	17m 36s
R-CMD-check / ubuntu-latest (release)	14m 3s
R-CMD-check / ubuntu-latest (oldrel)	15m 15s
R-CMD-check / ubuntu-latest (oldrel-2)	14m 2s
R-CMD-check / ubuntu-latest (oldrel-3)	14m 33s
R-CMD-check / ubuntu-latest (3.6)	5m 25s
	2h 43m 59s

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