chore(deps): update actions/checkout action to v4 #366

Job	Run time
Publish Charm / Generate the Charm Matrix	5s
Run Tests / Integration Test	15m 30s
Run Tests / Charm-specific Integration tests (microk8s) (tensorboard-controller)	17m 36s
Run Tests / Lint Check (tensorboard-controller)	18s
Run Tests / Charm-specific Integration tests (microk8s) (tensorboards-web-app)	19m 9s
Run Tests / Lint Check (tensorboards-web-app)	15s
Run Tests / Unit Test (tensorboard-controller)	18s
Run Tests / Unit Test (tensorboards-web-app)	21s
Run Tests / Check libraries (tensorboard-controller) / Check libraries	25s
Run Tests / Check libraries (tensorboard-controller) / Lint	9s
Run Tests / Check libraries (tensorboards-web-app) / Check libraries	26s
Run Tests / Check libraries (tensorboards-web-app) / Lint	11s
Run Tests / Terraform (tensorboard-controller) / Apply	0s
Run Tests / Terraform (tensorboards-web-app) / Apply	0s
Run Tests / Terraform (tensorboard-controller) / Check / Check Terraform	11s
Run Tests / Terraform (tensorboards-web-app) / Check / Check Terraform	9s
Run Tests / Terraform (tensorboards-web-app) / Lint / Lint Terraform	9s
Run Tests / Terraform (tensorboard-controller) / Lint / Lint Terraform	6s
Publish Charm / Publish Charm (./charms/tensorboard-controller)	7m 32s
Publish Charm / Publish Charm (./charms/tensorboards-web-app)	7m 19s
	1h 10m 9s

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