CI: Only run on the oldest and newest supported versions of Python

In order to save resources.

Author: amotl

.github/workflows/tests.yml

@@ -26,7 +26,7 @@ jobs:
     strategy:
       matrix:
         os: [ "ubuntu-latest" ]
-        python-version: [ "3.7", "3.8", "3.9", "3.10", "3.11" ]
+        python-version: [ "3.7", "3.11" ]
         grafana-version: [ "6.7.6", "7.5.17", "8.5.15", "9.2.7" ]
 
     env: