Update supported versions of Ruby

- description in README
- version for test in CI

Author: kotp

.github/workflows/exercise-tests.yml

@@ -16,7 +16,7 @@ jobs:
       matrix:
         os:
           - ubuntu-24.04
-        ruby-version: [3.2, 3.3]
+        ruby-version: [3.4]
 
     steps:
       - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3

README.md

@@ -19,9 +19,11 @@ Exercism Exercises in Ruby
 
 ## Setup
 
-You'll need a recent (2.6+) version of Ruby, but that's it.
+You will want a recent (3.4+) version of Ruby, but that's it.
 Minitest ships with the language, so you're all set.
 
+Older versions of Ruby may work, but are not officially supported.
+
 ## Anatomy of an Exercise
 
 The files for an exercise live in `exercises/<slug>`.