test: use fixed Python version 3.10

Author: dmyger

.github/workflows/tests.yml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 
 env:
   GO_VERSION: 1.14
-  PYTHON_VERSION: '3.x'
+  PYTHON_VERSION: '3.10'
 
 jobs:
   tests:
@@ -55,4 +55,4 @@ jobs:
       - name: Integration tests
         run:  |
           source ./venv/bin/activate
-          make integration
+          make integration