GHA: Check against R 3.5.0 #752

Job	Run time
windows-latest (devel)	8m 7s
windows-latest (release)	9m 26s
windows-latest (oldrel)	10m 0s
macOS-latest (devel)	9m 31s
macOS-latest (release)	9m 8s
macOS-latest (oldrel)	9m 50s
ubuntu-latest (devel)	7m 10s
ubuntu-latest (release)	6m 17s
ubuntu-latest (oldrel)	6m 0s
ubuntu-latest (oldrel-1)	8m 2s
ubuntu-latest (oldrel-2)	6m 12s
ubuntu-latest (3.5)	6m 29s
ubuntu-latest (3.4)	7m 24s
ubuntu-latest (release) ko	6m 6s
ubuntu-latest (release) zh_CN	6m 8s
ubuntu-latest (release) zh_TW	8m 21s
ubuntu-latest (release) keepWhere	6m 1s
ubuntu-latest (release) !keepWhere	7m 34s
ubuntu-latest (release) multicore, no-multithreading-in-forks	6m 26s
ubuntu-latest (release) multisession, no-multithreading-in-forks	7m 10s
ubuntu-latest (release) no-immediate-relay-in-psock	7m 38s
	2h 39m 0s

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