[MISC] Update microk8s to 1.28 #963

Job	Run time
Unit tests	35s
Check libraries	37s
Lint	29s
Build charms / Get workflow version / Get workflow version	3s
Build charms / Collect charms	15s
Build charms / Build pgbouncer-k8s charm \| 22.04	2m 26s
Build charms / Build application charm \| 22.04	1m 58s
backend-integration \| 2.9.44	17m 34s
backend-integration \| 3.1.5	22m 1s
client-relation-integration \| 2.9.44	24m 20s
client-relation-integration \| 3.1.5	24m 19s
scaling-integration \| 2.9.44	19m 1s
scaling-integration \| 3.1.5	24m 20s
tls-integration \| 2.9.44	6m 25s
tls-integration \| 3.1.5	1m 39s
standalone-integration \| 2.9.44	43s
standalone-integration \| 3.1.5	1s
legacy-client-relation-integration \| 2.9.44	1s
legacy-client-relation-integration \| 3.1.5	1s
	2h 26m 48s

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