CI: Add Ruby 3.3/3.4 for CI

Signed-off-by: Kentaro Hayashi <[email protected]>

Author: kenhys

.github/workflows/linux.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['2.7', '3.0', '3.1', '3.2']
+        ruby: ['2.7', '3.0', '3.1', '3.2', '3.3', '3.4']
         os:
           - ubuntu-latest
         experimental: [false]