Update main.yml

.github/workflows/main.yml

@@ -30,6 +30,7 @@ jobs:
       - uses: actions/setup-python@v4
         with:
           python-version: '3.9'
+      - run: pip install --upgrade pip
       # install dependencies listed in requirements.txt file
       - run: pip install -r requirements.txt
       # deploy mkdocs to github pages