Remove Python 3.6, 3.7 from test matrix, add 3.10

Author: nikmolnar

.github/workflows/python-package.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9]
+        python-version: [3.8, 3.9, 3.10]
         celery-version: [4.*, 5.*]
         django-version: [2.2, 3.2, 4.0]