docker: use ubi-micro base image #1679

Job	Run time
govet (1.21.x, ubuntu-latest)	3m 22s
lint (1.21.x, ubuntu-latest)	5m 16s
Shellcheck (1.21.x)	35s
Check for vulnerable dependencies (1.21.x)	1m 1s
operator (1.21.x, ubuntu-latest)	5m 8s
gotest (1.21.x, ubuntu-latest)	3m 22s
test-policy-binding (1.21.x, ubuntu-latest)	11m 18s
helm-floor (1.21.x, ubuntu-latest)	3m 44s
test-kes (1.21.x, ubuntu-latest)	5m 37s
test-tenant (1.21.x, ubuntu-latest)	4m 1s
test-tenant-upgrade (1.21.x, ubuntu-latest)	4m 49s
helm (1.21.x, ubuntu-latest)	3m 10s
	51m 23s

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