Update main.yml

.github/workflows/main.yml

@@ -27,6 +27,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         python -m pip install flake8 pytest
+        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
         if [ -f doc-requirements.txt ]; then pip install -r doc-requirements.txt; fi
     - name: Build html
       run: |