Deprecate testing in Ruby 3.1

As of July 30th 2025 it's out of a maintianance window
https://www.ruby-lang.org/en/downloads/branches/

Author: huwd

.github/workflows/test.yaml

@@ -1,6 +1,6 @@
 name: Test
 
-on: 
+on:
   push:
     branches:
       - main
@@ -14,7 +14,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby: ['3.1', '3.2', '3.3']
+        ruby: ['3.2', '3.3']
 
     steps:
       - uses: actions/checkout@v4