Add Ruby 3.4 to build (rubyjs#339)

Author: tisba

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
         os:
           - "macos-13"
           - "macos-14" # arm64
-          - "macos-15"
+          - "macos-15" # arm64
           - "ubuntu-20.04"
         ruby:
           - "truffleruby+graalvm"
@@ -58,6 +58,7 @@ jobs:
           - "ruby-3.1"
           - "ruby-3.2"
           - "ruby-3.3"
+          - "ruby-3.4"
 
     name: ${{ matrix.os }} - ${{ matrix.ruby }}
     runs-on: ${{ matrix.os }}
@@ -88,6 +89,7 @@ jobs:
           - "3.1"
           - "3.2"
           - "3.3"
+          - "3.4"
         platform:
           - "amd64"
           - "arm64"