chore(deps): update actions/checkout action to v4 #686

Job	Run time
Publish Charm / Generate the Charm Matrix	5s
Run Tests / Lint	16s
Run Tests / Integration tests (microk8s) (katib-controller)	40m 52s
Run Tests / Test the bundle	1h 50m 28s
Run Tests / Integration tests (microk8s) (katib-db-manager)	38m 36s
Run Tests / Unit tests (katib-controller)	28s
Run Tests / Unit tests (katib-db-manager)	17s
Run Tests / Check libraries (katib-controller) / Check libraries	22s
Run Tests / Check libraries (katib-controller) / Lint	11s
Run Tests / Check libraries (katib-db-manager) / Check libraries	33s
Run Tests / Check libraries (katib-db-manager) / Lint	10s
Run Tests / Check libraries (katib-ui) / Check libraries	27s
Run Tests / Check libraries (katib-ui) / Lint	11s
Publish Charm / Publish Charm (./charms/katib-ui)	21m 45s
Publish Charm / Publish Charm (./charms/katib-controller)	30m 44s
Publish Charm / Publish Charm (./charms/katib-db-manager)	28m 36s
	4h 34m 1s

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