ci: skip collection of debug artefacts on success

The Github runners for the KFP CI are getting out of storage by the
time the tests execution finishes, so there is no space left for saving
logs. Skipping saving the debug artefacts on success will allow the workflows
to run successfully.

.github/workflows/integrate.yaml

@@ -179,6 +179,8 @@ jobs:
         run: juju status
         if: failure()
 
+      # Collect debug artefacts only on failure as the CI for this repository
+      # in particular struggles with storage limitations.
       - name: Collect charm debug artifacts
         uses: canonical/kubeflow-ci/actions/dump-charm-debug-artifacts@main
-        if: always()
+        if: failure()