python-openapi/openapi-core#296: Drop python 3.6 support

Author: nezhar

.github/workflows/python-test.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9]
+        python-version: [3.7, 3.8, 3.9]
       fail-fast: false
     steps:
       - uses: actions/checkout@v2