also run tests for 'eb' command with Python 3.10

Author: boegel

.github/workflows/eb_command.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        python: [2.7, 3.5, 3.6, 3.7, 3.8, 3.9]
+        python: [2.7, 3.5, 3.6, 3.7, 3.8, 3.9, '3.10']
       fail-fast: false
     steps:
     - uses: actions/checkout@v2