ci: use merge-gatekeeper #19

Job	Run time
build / build-container (frontend, frontend/Containerfile, frontend/)	2m 13s
build / build-container (reis, services/reis/Containerfile, services/reis/)	43s
build / build-container (backend, Containerfile.backend, .)	1m 46s
reis-stresstest / test-stress	6m 56s
e2e (chromium, extension-tests) / run-e2e	4m 10s
e2e (firefox, expensive-tests) / run-e2e	2m 6s
e2e (chromium, expensive-tests) / run-e2e	2m 4s
e2e (webkit, expensive-tests) / run-e2e	2m 25s
e2e (firefox, extension-tests) / run-e2e	6m 29s
e2e (webkit, extension-tests) / run-e2e	8m 10s
e2e (webkit, tests) / run-e2e	4m 21s
e2e (chromium, tests) / run-e2e	2m 53s
e2e (firefox, tests) / run-e2e	5m 27s
	49m 43s

Provide feedback