Deploy docs action fix branch name extraction

.github/workflows/deploy_docs.yml

@@ -30,17 +30,13 @@ jobs:
       - name: Generate docs
         run: dart doc
 
-      - name: Extract branch name
-        shell: bash
-        run: echo "##[set-output name=branch;]$(echo ${GITHUB_REF#refs/heads/})"
-        id: extract_branch
-
       - name: Deploy nyxx dev docs
         uses: easingthemes/[email protected]
         env:
+          BRANCH_NAME: ${{ github.head_ref || github.ref_name }}
           ARGS: "-rltDzvO"
           SOURCE: "doc/api/"
-          TARGET: "${{ secrets.DEPLOY_REMOTE_TARGET }}/dartdocs/nyxx/${{ steps.extract_branch.outputs.branch }}/"
+          TARGET: "${{ secrets.DEPLOY_REMOTE_TARGET }}/dartdocs/nyxx/${{ env.BRANCH_NAME }}/"
         with:
           REMOTE_HOST: ${{ secrets.DEPLOY_REMOTE_HOST }}
           REMOTE_USER: ${{ secrets.DEPLOY_REMOTE_USER }}