ci: change python version in ci

Author: ar90n

.github/workflows/ci-testing.yml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04]
-        python-version: ["3.10"]
+        python-version: ["3.7"]
     # Timeout: https://stackoverflow.com/a/59076067/4521646
     timeout-minutes: 35