ci: bump juju to 3.6 + charmcraft to 3.x/stable (#67)

* Bump juju to 3.6/stable
* For uniformity, use charmcraft from 3.x/stable

Ref canonical/bundle-kubeflow#1176

.github/workflows/integrate.yaml

@@ -73,10 +73,11 @@ jobs:
     - name: Setup operator environment
       uses: charmed-kubernetes/actions-operator@1.1.0
       with:
-        juju-channel: 3.4/stable
+        juju-channel: 3.6/stable
         provider: microk8s
         channel: 1.29-strict/stable
         microk8s-addons: "dns hostpath-storage rbac metallb:10.64.140.43-10.64.140.49"
+        charmcraft-channel: 3.x/stable
 
     # Running with kubeflow model because of upstream issue https://github.com/kubeflow/kubeflow/issues/7283
     - name: Run integration tests