chore(backport-1.18): Pin charmcraft channel to `3.x/stable` #1188

Job	Run time
Run Tests / Observability Integration Test (1.25-strict/stable)	55m 24s
Publish Charm / Generate the Charm Matrix	3s
Run Tests / Integration Test (1.25-strict/stable, integration)	1h 0m 16s
Run Tests / Observability Integration Test (1.26-strict/stable)	56m 40s
Run Tests / Lint Code (pilot)	22s
Run Tests / Integration Test (1.25-strict/stable, integration-tls-provider)	57m 12s
Run Tests / Unit Test (pilot)	1m 22s
Run Tests / Unit Test (gateway)	30s
Run Tests / Lint Code (gateway)	21s
Run Tests / Integration Test (1.25-strict/stable, integration-tls-secret)	56m 26s
Run Tests / Integration Test (1.27-strict/stable, integration)	59m 41s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-provider)	1h 4m 15s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-secret)	1h 0m 46s
Run Tests / Check libraries (istio-gateway) / Check libraries	5s
Run Tests / Check libraries (istio-gateway) / Lint	8s
Run Tests / Check libraries (istio-pilot) / Check libraries	26s
Run Tests / Check libraries (istio-pilot) / Lint	12s
Publish Charm / Publish Charm (./charms/istio-pilot)	40m 9s
Publish Charm / Publish Charm (./charms/istio-gateway)	15m 18s
	8h 49m 36s

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