ci: add prune job so failing variants still get cleaned up

.gitea/workflows/build.yaml

@@ -119,3 +119,26 @@ jobs:
           buildid="$(cat .buildid)"
           pkgs="build/${IMAGE}-${DISTRO}-${ARCH}/packages-current.txt"
           ./release.sh "${IMAGE}" "${DISTRO}" "${buildid}" "${pkgs}"
+
+  prune:
+    name: Prune old releases
+    runs-on: job-v2
+    needs: build
+    # Run even if some matrix builds failed (e.g. rawhide churn), so their old
+    # releases still get cleaned up.
+    if: ${{ always() && github.event_name != 'pull_request' }}
+    container:
+      image: "quay.io/fedora-ostree-desktops/buildroot:44"
+      options: "--security-opt=label=disable --privileged --user 0:0"
+    env:
+      GITEA_URL: https://git.plabble.org
+      GITEA_REPO: Misthios/bootc-images
+    steps:
+      - name: Install tools
+        run: dnf install -y nodejs jq curl
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Prune old releases
+        env:
+          RELEASE_TOKEN: ${{ secrets.RELEASE_TOKEN }}
+        run: ./prune-releases.sh fedora-cosmic