Adjust gitpod setup steps (#1717) #1280

Job	Run time
lint_theme	45s
set_sites	48s
test_phpunit	1m 33s
test_new_site	13m 19s
test_existing_site (art)	7m 41s
test_existing_site (dlcl)	10m 21s
test_existing_site (dsresearch)	5m 52s
test_existing_site (em1060)	6m 9s
test_existing_site (hps)	6m 44s
test_existing_site (hs_colorful)	7m 32s
test_existing_site (it_humsci2023)	5m 55s
test_existing_site (linguistics)	7m 56s
test_existing_site (philit)	8m 0s
test_existing_site (southasia)	7m 14s
deploy_branch	1m 49s
	1h 31m 38s

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