Drop tests (but not compatibility) for python 3.6 due to test depende…

…ncy 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