ci: try to fixup the artifact name for upload

.github/workflows/ubuntu.yml

@@ -85,10 +85,13 @@ jobs:
       run: "./assets/build-deb.sh"
     - name: Verify Package is installable
       run: "apt-get install ./kumomta*.deb"
+    - name: Make artifact name
+      id: artifact-name
+      run: echo "name=${{ matrix.container }}" | tr ':' '-' >> $GITHUB_OUTPUT
     - name: "Upload artifact"
       uses: actions/upload-artifact@v3
       with:
-        name: ${{ matrix.container }}
+        name: ${{ steps.artifact-name.outputs.name }}
         path: "kumomta*.deb"
     - name: "Publish"
       if: ${{ github.ref == 'refs/heads/main' }}