Update Python version matrix in GitHub actions

The matrix of Python versions in the GitHub Actions configuration has been revised. Python 3.10 has been removed, and the process will now only use Python 3.8 and 3.9 for running the unit tests.

.github/workflows/unittest.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       max-parallel: 4
       matrix:
-        python-version: [3.8, 3.9, 3.10]
+        python-version: [3.8, 3.9]
 
     steps:
     - uses: actions/checkout@v3