Add py3.6-3.7 to test matrix

Author: kalekseev

.github/workflows/main.yml

@@ -29,6 +29,11 @@ jobs:
           - drf: djangorestframework
             python-version: "3.10"
             django-version: "Django<4.2,>=4.1" # must be different from django-version
+          - django-version: "Django<4.0,>=3.2"
+            python-version: 3.6
+          - django-version: "Django<4.0,>=3.2"
+            python-version: 3.7
+
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4