Update Github action workflow to add CI testing for Ruby versions 3.1…

… and 3.2

and drop version 2.5 since:
- the CI bundler build step does not seem to support it anymore
- It is a truly ancient version now as well; official support for 2.5
  from the Ruby lang teaam has ended long ago.

.github/workflows/run_tests.yaml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.5', '2.6', '2.7', '3.0']
+        ruby-version: ['2.6', '2.7', '3.0', '3.1', '3.2']
 
     steps:
     - uses: actions/checkout@v3