Add cache option to setup action #344

Job	Run time
static	3m 31s
test (docs)	3m 0s
test (examples)	3m 16s
test (test, test local var val, --test-arg --test-arg)	1m 16s
test (remote, 0)	3m 23s
test (remote-test, remote-test, 1)	3m 41s
test (test-coverage, test local var val, --test-arg, test-coverage)	1m 10s
test (test-coverage, test local var val, --test-arg, 3.8, ubuntu-20.04, test-coverage-oldest)	1m 25s
test (test-nengo, test local var val, --test-arg, 3.11)	1m 58s
deploy	0s
coverage	1m 6s
auto-update	2m 38s
	26m 24s

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