TARGET_FOLDER is not an env, so we need to give it a value.

.github/workflows/docs_release.yml

@@ -4,41 +4,50 @@ on:
   release:
     types: [ created ]
 
+env:
+  VERSION_FILE: recipipe/_version.py
+
 jobs:
   docs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+
     - name: Set up Python 3.7
       uses: actions/setup-python@v2
       with:
         python-version: 3.7
+
     - name: Update version
       run: |
         # Get version numbers form GITHUB_REF (without the leading "v").
         VERSION=$(sed -n 's/.*\/v\(.*\)/\1/p' <<< $GITHUB_REF)
         # Substitute value in _version file.
-        sed -i "s/0.0.0/$VERSION/" recipipe/_version.py
+        sed -i "s/0.0.0/$VERSION/" $VERSION_FILE
         # Save a version env variable to reuse it later (leading "v" included).
-        # This variable is used by JamesIves/github-pages-deploy-action
-        # and indicates the output folder where the docs are going to be saved.
-        echo ::set-env name=TARGET_FOLDER::v$VERSION
+        echo ::set-env name=RELEASE_VERSION::v$VERSION
+
     - name: Install dependencies
       run: |
         sudo apt-get install graphviz
         pip install -r requirements_dev.txt
+
     - name: Generate pre-build data
       run: |
         cd doc/
         make generate_data
+
     - name: Build docs
       run: |
         cd doc/
         make html
         touch _build/html/.nojekyll  # needed to deploy folders starting with "_" in gh-pages
+
     - name: Deploy to gh-pages
       uses: JamesIves/github-pages-deploy-action@releases/v3
       with:
         ACCESS_TOKEN: ${{ secrets.ACCESS_TOKEN }}
         BRANCH: gh-pages  # the branch the action should deploy to.
         FOLDER: doc/_build/html  # the folder the action should deploy.
+        # Output folder where the docs are going to be saved.
+        TARGET_FOLDER: ${{ env.RELEASE_VERSION }}