Drop tests (but not package metadata) for python 3.6 due to test depe…

…ndency issues

Main dependencies aren't affected, so we'll retain package support for 3.6 for now, just without automated tests.

.github/workflows/build.yml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9, '3.10']
+        python-version: [3.7, 3.8, 3.9, '3.10']
 
     steps:
       - uses: actions/checkout@v2