Builds for Python 3.6 no longer work; disable them (#672)

Author: pietern

.github/workflows/push.yml

@@ -11,7 +11,6 @@ jobs:
     strategy:
       matrix:
         python-version:
-          - '3.6'
           - '3.7'
           - '3.8'
           - '3.9'
@@ -62,7 +61,7 @@ jobs:
     strategy:
       matrix:
         python-version:
-          - '3.6'
+          - '3.7'
     env:
       PYTHON_VERSION: ${{ matrix.python-version }}
     steps: