Wrap 3.10 in quotes so that it is interpreted correctly

Author: dstricks

.github/workflows/test.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-20.04, windows-latest, macos-latest]
-        python-version: [3.6, 3.7, 3.8, 3.9, 3.10]
+        python-version: [3.6, 3.7, 3.8, 3.9, "3.10"]
 
     steps:
       - name: Checkout repository