Fix CI: Remove Ruby 3.1 from matrix since plugin requires Ruby 3.2+

Co-authored-by: PowerKiKi <[email protected]>

Author: Copilot

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby: ['3.1', '3.2', '3.3']
+        ruby: ['3.2', '3.3']
         redmine: ['6.0-stable', 'master']
         db: ['postgres', 'mysql']
       fail-fast: false