Correction of version in test_main.yml

The python version 3.10 was changed to '3.10'

Author: snag427

.github/workflows/test_main.yml

@@ -20,7 +20,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: 3.10
+          python-version: '3.10'
 
       - name: Install dependencies
         run: |