Work directly on gh-pages branch to generate the API documentation.

.github/workflows/publish_api_documentation.yml

@@ -15,10 +15,13 @@ jobs:
     - uses: actions/checkout@v2
       with:
         fetch-depth: 0
-        ref: "3.0"
+        ref: "gh-pages"
     - uses: actions/setup-python@v2
       with:
         python-version: 3.6
+    - name: Merge changes from 3.0 branch
+      run: |
+        git merge 3.0 -X theirs
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
@@ -37,6 +40,4 @@ jobs:
         git add docs
         git status
         git commit -m "Publish API documentation"
-        git checkout gh-pages
-        git merge 3.0 -X theirs
         git push