Simplify branch retrieval

.github/workflows/ci.yml

@@ -86,10 +86,6 @@ jobs:
     container:
       image: "kiwix/kiwix-build_ci:${{matrix.image_variant}}-31"
     steps:
-    - name: Extract branch name
-      shell: bash
-      run: echo "##[set-output name=branch;]$(echo ${GITHUB_REF#refs/heads/})"
-      id: extract_branch
     - name: Checkout code
       shell: python
       run: |
@@ -99,7 +95,7 @@ jobs:
           'git', 'clone',
           'https://github.com/${{github.repository}}',
           '--depth=1',
-          '--branch', ${{steps.extract_branch.outputs.branch}}'
+          '--branch', '${{ github.head_ref || github.ref_name }}'
         ]
         check_call(command, cwd=environ['HOME'])
     - name: Install deps