ci: use microk8s strict and pin juju version (#122)

* ci: use microk8s strict and pin juju version

To keep consistency with the CKF owned repositories, we must pin the juju version
to 3.1/stable, and install microk8s in strict mode to allow bootstraping juju 3.x
controllers. This commit also pins microk8s to v1.25.

.github/workflows/on_pull_request.yaml

@@ -41,13 +41,10 @@ jobs:
       uses: charmed-kubernetes/actions-operator@main
       with:
         provider: microk8s
-        channel: 1.24/stable
+        channel: 1.25-strict/stable
+        juju-channel: 3.1/stable
         charmcraft-channel: latest/candidate
         microk8s-addons: "dns storage rbac metallb:10.64.140.43-10.64.140.49"
-    # TODO: Remove once the actions-operator does this automatically
-    - name: Configure kubectl
-      run: |
-        sg microk8s -c "microk8s config > ~/.kube/config"
 
     - name: Add model
       run: |