chore(ci): install prometheus operator CRDs in order to be able to te…

…st ServiceMonitors / PrometheusRules / etc validity in charts. (#4715)

.github/workflows/lint-test.yaml

@@ -29,6 +29,7 @@ jobs:
           changed="$(ct list-changed --config .github/linters/ct.yaml)"
           if [[ -n "$changed" ]]; then
             echo "changed=true" >> "$GITHUB_OUTPUT"
+            echo "changed_list=\"${changed//$'\n'/ }\"" >> "$GITHUB_OUTPUT"
           fi
 
       # - name: install helm unittest plugin
@@ -48,5 +49,18 @@ jobs:
         run: kubectl apply -k https://github.com/kubernetes-sigs/gateway-api/config/crd
         if: steps.list-changed.outputs.changed == 'true'
 
+      - name: Apply Prometheus Operator CRDs (unless for charts already installing it)
+        env:
+          CHANGED_LIST: ${{ steps.list-changed.outputs.changed_list }}
+        run: |
+          # Always run unless only changed chart is one of impacted charts
+          echo "List is: $CHANGED_LIST"
+          if [ "$CHANGED_LIST" = '"charts/kube-prometheus-stack"' ] || [ "$CHANGED_LIST" = '"charts/prometheus-operator-crds"' ]; then
+            echo "Skipping install"
+          else
+            helm install prometheus-operator-crds oci://ghcr.io/prometheus-community/charts/prometheus-operator-crds
+          fi
+        if: steps.list-changed.outputs.changed == 'true'
+
       - name: Run chart-testing (install)
         run: ct install --config .github/linters/ct.yaml