Add support for Python 3.10 RC

Author: bcantoni

.github/workflows/run-tests.yml

@@ -8,7 +8,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9]
+        python-version: [3.5, 3.6, 3.7, 3.8, 3.9, 3.10.0-rc.2]
 
     runs-on: ${{ matrix.os }}