ci: update test matrix

Author: rubysamurai

.github/workflows/ci.yml

@@ -5,10 +5,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest]
-        ruby: ['2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', head, truffleruby, truffleruby-head]
-    runs-on: ${{ matrix.os }}
-    name: Ruby ${{ matrix.ruby }} on ${{ matrix.os }}
+        ruby: ['2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', '3.4', head, truffleruby, truffleruby-head]
+    runs-on: ubuntu-latest
+    name: Ruby ${{ matrix.ruby }}
     steps:
       - name: Checkout
         uses: actions/checkout@v4