Deprecate Python 3.6

Based on actions/setup-python#544, python 3.6 is no longer supported on ubuntu-latest

Author: mgmacias95

.github/workflows/testing.yaml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9]
+        python-version: [3.7, 3.8, 3.9, 3.10]
 
     steps:
       - uses: actions/checkout@v3