Test with ruby head

Author: nobu

.github/workflows/ci.yml

@@ -59,7 +59,7 @@ jobs:
       fail-fast: false
       matrix:
         # Test against all versions supported by rubygems
-        ruby_version: ["2.7", "3.0", "3.1", "3.2", "3.3", "3.4", "4.0"]
+        ruby_version: ["2.7", "3.0", "3.1", "3.2", "3.3", "3.4", "4.0", "head"]
         sys:
           - os: ubuntu-latest
             rust_toolchain: ${{ needs.fetch_ci_data.outputs.minimum-supported-rust-version }}