Test only on Ruby head

Author: noteflakes

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
       matrix:
         # macos-latest uses arm64, macos-13 uses x86
         os: [ubuntu-latest]
-        ruby: ['3.4', 'head']
+        ruby: ['head']
 
     name: ${{matrix.os}}, ${{matrix.ruby}}