Update unit tests base image

Ubuntu 20.04 images have been deprecated, so when the unit
tests job is executed GH fails to find available runners.

Use Ubuntu 22.04 as base image for the unit tests job to fix
this issue.

Author: vkmc

.github/workflows/unit_tests.yml

@@ -31,7 +31,7 @@ on:
 jobs:
   test-framework:
     name: Unit test suite
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
 
     steps:
       - name: Checkout code