Fix mkdir + branch name

.github/workflows/firecracker.yml

@@ -23,15 +23,13 @@ jobs:
       - name: Build FC versions
         run: |
           # The format will be: latest_tag-branch-latest_commit_hash — v1.7.0-dev_g8bb88311
-          echo "$(git show-ref --tags -d)"
-
           git fetch --prune --unshallow
           latest_tag=$(git describe --tags --abbrev=0 HEAD~)
           echo "Latest Tag: $latest_tag"
 
-          version_name=$(git describe --tags --abbrev=0 ${{ github.head_ref }})-${{ github.head_ref }}_${{ github.sha }}
+          version_name="$latest_tag-${GITHUB_HEAD_REF:-${GITHUB_REF#refs/heads/}}_${{ github.sha }}"
           echo "Version name: $version_name"
-          mkdir "builds/${version_name}"
+          mkdir -p "builds/${version_name}"
 
           echo "Building Firecracker version: $version_name"
           tools/devtool -y build --release