Fixed CI build

Author: bastianeicher

.github/workflows/publish.yml

@@ -8,10 +8,6 @@ jobs:
     steps:
       - name: Clone repo
         uses: actions/checkout@v2
-      - name: Set up Python
-        uses: actions/setup-python@v1
-        with:
-          python-version: 3.8.x
       - name: Install mkdocs
         run: pip install -r requirements.txt
       - name: Build documentation