Remove Python 3.6, 3.7 and 3.8 from GitHub Actions workflow.

Author: andrii-porokhnavets

.github/workflows/main.yml

@@ -13,7 +13,6 @@ jobs:
           - "windows-latest"
           - "macos-latest"
         python:
-          - "3.8"
           - "3.9"
           - "3.10"
           - "3.11"