chore(deps): update actions/checkout action to v4 #734

Job	Run time
Run Tests / Bundle Integration	24m 27s
Publish Charm / Generate the Charm Matrix	6s
Run Tests / Individual charm's integration tests (controller)	20m 5s
Run Tests / Individual charm's integration tests (ui)	15m 16s
Run Tests / Lint Code (controller)	36s
Run Tests / Lint Code (ui)	27s
Run Tests / Unit Test (controller)	57s
Run Tests / Unit Test (ui)	47s
Run Tests / Check libraries (jupyter-ui) / Check libraries	28s
Run Tests / Check libraries (jupyter-controller) / Lint	14s
Run Tests / Check libraries (jupyter-controller) / Check libraries	33s
Run Tests / Check libraries (jupyter-ui) / Lint	14s
Publish Charm / Publish Charm (./charms/jupyter-ui)	6m 8s
Publish Charm / Publish Charm (./charms/jupyter-controller)	4m 27s
	1h 14m 45s

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