chore(deps): update actions/checkout action to v4 #988

Job	Run time
Publish Charm / Generate the Charm Matrix	3s
Run Tests / Individual charm's integration tests (controller)	17m 37s
Run Tests / Individual charm's integration tests (ui)	15m 27s
Run Tests / Lint Code (controller)	21s
Run Tests / Lint Code (ui)	21s
Run Tests / Unit Test (controller)	26s
Run Tests / Unit Test (ui)	25s
Run Tests / Bundle Integration	20m 47s
Run Tests / Check libraries (jupyter-controller) / Check libraries	25s
Run Tests / Check libraries (jupyter-controller) / Lint	8s
Run Tests / Check libraries (jupyter-ui) / Check libraries	25s
Run Tests / Check libraries (jupyter-ui) / Lint	8s
Run Tests / Terraform (controller) / Apply / Apply Terraform	5m 1s
Run Tests / Terraform (controller) / Check / Check Terraform	5s
Run Tests / Terraform (controller) / Lint / Lint Terraform	9s
Run Tests / Terraform (ui) / Apply / Apply Terraform	5m 32s
Run Tests / Terraform (ui) / Check / Check Terraform	6s
Run Tests / Terraform (ui) / Lint / Lint Terraform	8s
Publish Charm / Publish Charm (./charms/jupyter-ui)	7m 3s
Publish Charm / Publish Charm (./charms/jupyter-controller)	7m 4s
	1h 21m 41s

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