chore(deps): update actions/checkout action to v4 #887

Job	Run time
Publish Charm / Generate the Charm Matrix	2s
Run Tests / Bundle Integration	16m 0s
Run Tests / Individual charm's integration tests (controller)	13m 3s
Run Tests / Individual charm's integration tests (ui)	13m 40s
Run Tests / Unit Test (controller)	23s
Run Tests / Lint Code (controller)	21s
Run Tests / Unit Test (ui)	26s
Run Tests / Lint Code (ui)	31s
Run Tests / Check libraries (jupyter-controller) / Check libraries	36s
Run Tests / Check libraries (jupyter-controller) / Lint	8s
Run Tests / Check libraries (jupyter-ui) / Check libraries	29s
Run Tests / Check libraries (jupyter-ui) / Lint	9s
Publish Charm / Publish Charm (./charms/jupyter-ui)	4m 6s
Publish Charm / Publish Charm (./charms/jupyter-controller)	3m 46s
	53m 40s

Provide feedback