fix: checkout maintenance op repo in the release pipeline (#1657)

otherwise we can't check for helm chart updates

Author: almaslennikov

.github/workflows/release.yaml

@@ -213,6 +213,11 @@ jobs:
           repository: ${{ github.repository_owner }}/node-feature-discovery
           path: node-feature-discovery
           ref: ${{ needs.determine-versions.outputs.release_branch }}
+      - uses: actions/checkout@v4
+        with:
+          repository: ${{ github.repository_owner }}/maintenance-operator
+          path: maintenance-operator
+          ref: ${{ needs.determine-versions.outputs.release_branch }}
       - uses: actions/checkout@v4
         with:
           repository: ${{ github.repository_owner }}/network-operator