feat(ci): Test kernel signing against Ublue base image

.github/workflows/test-action.yml

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+name: Test Action
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+env:
+  IMAGE_REGISTRY: ghcr.io/${{ github.repository_owner }}
+
+jobs:
+  push-ghcr:
+    name: Test
+    runs-on: ubuntu-22.04
+    permissions:
+      contents: read
+      packages: write
+      id-token: write
+    strategy:
+      fail-fast: false
+      matrix:
+        image_name: [kernel-signer-test]
+    steps:
+      # Checkout push-to-registry action GitHub repository
+      - name: Checkout Push to Registry action
+        uses: actions/checkout@v4
+
+      - name: Generate tags
+        id: generate-tags
+        shell: bash
+        run: |
+          # Generate a timestamp for creating an image version history
+          TIMESTAMP="$(date +%Y%m%d)"
+          COMMIT_TAGS=()
+          BUILD_TAGS=()
+          # Have tags for tracking builds during pull request
+          SHA_SHORT="${GITHUB_SHA::7}"
+          COMMIT_TAGS+=("pr-${{ github.event.pull_request.number }}")
+          COMMIT_TAGS+=("${SHA_SHORT}")
+
+          BUILD_TAGS=("latest" "${TIMESTAMP}")
+
+          if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+              echo "Generated the following commit tags: "
+              for TAG in "${COMMIT_TAGS[@]}"; do
+                  echo "${TAG}"
+              done
+              alias_tags=("${COMMIT_TAGS[@]}")
+          else
+              alias_tags=("${BUILD_TAGS[@]}")
+          fi
+          echo "Generated the following build tags: "
+          for TAG in "${BUILD_TAGS[@]}"; do
+              echo "${TAG}"
+          done
+          echo "alias_tags=${alias_tags[*]}" >> $GITHUB_OUTPUT
+
+      # Build metadata
+      - name: Image Metadata
+        uses: docker/metadata-action@v5
+        id: meta
+        with:
+          images: |
+            ${{ matrix.image_name }}
+          labels: |
+            org.opencontainers.image.title=${{ matrix.image_name }}
+            org.opencontainers.image.version=latest
+            org.opencontainers.image.description=Test Action.
+            io.artifacthub.package.readme-url=https://github.com/${{ github.repository_owner }}/kernel-signer#readme
+
+      # Build image using Buildah action
+      - name: Build Image
+        id: build_image
+        uses: redhat-actions/buildah-build@v2
+        with:
+          containerfiles: |
+            ./Containerfile
+          image: ${{ matrix.image_name }}
+          tags: |
+            ${{ steps.generate-tags.outputs.alias_tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          oci: true
+          extra-args: |
+            --target=${{ matrix.image_name }}
+
+      # Workaround bug where capital letters in your GitHub username make it impossible to push to GHCR.
+      # https://github.com/macbre/push-to-ghcr/issues/12
+      - name: Lowercase Registry
+        id: registry_case
+        uses: ASzc/change-string-case-action@v6
+        with:
+          string: ${{ env.IMAGE_REGISTRY }}
+
+      # Test kernel signing
+      - name: Sign kernel
+        uses: ./
+        with:
+          image: ${{ steps.build_image.outputs.image }}
+
+      # Push the image to GHCR (Image Registry)
+      - name: Push To GHCR
+        uses: redhat-actions/push-to-registry@v2
+        id: push
+        if: github.event_name != 'pull_request'
+        env:
+          REGISTRY_USER: ${{ github.actor }}
+          REGISTRY_PASSWORD: ${{ github.token }}
+        with:
+          image: ${{ steps.build_image.outputs.image }}
+          tags: ${{ steps.build_image.outputs.tags }}
+          registry: ${{ steps.registry_case.outputs.lowercase }}
+          username: ${{ env.REGISTRY_USER }}
+          password: ${{ env.REGISTRY_PASSWORD }}
+          extra-args: |
+            --disable-content-trust
+
+      - name: Sign image
+        uses: EyeCantCU/cosign-action/sign@v0.2.1
+        if: github.event_name != 'pull_request'
+        with:
+          container: ghcr.io/${{ github.repository_owner }}/${{ matrix.image_name }}
+          registry-token: ${{ secrets.GITHUB_TOKEN }}
+          signing-secret: ${{ secrets.SIGNING_SECRET }}
+          tags: ${{ steps.push.outputs.digest }}
+
+      - name: Echo outputs
+        if: github.event_name != 'pull_request'
+        run: |
+          echo "${{ toJSON(steps.push.outputs) }}"
+
+  check:
+    name: Check all builds successful
+    runs-on: ubuntu-latest
+    needs: [push-ghcr]
+    steps:
+      - name: Exit
+        shell: bash
+        run: exit 0

Containerfile

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+FROM ghcr.io/ublue-os/base-main:latest AS kernel-signer-test
+
+RUN ostree container commit