✅🚧 Run CI with TruffleRuby (experimental for now)

Using truffleruby-head to ensure we have several necessary bugfixes.

Author: nevans

.github/workflows/test.yml

@@ -20,6 +20,8 @@ jobs:
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
         os: [ ubuntu-latest, macos-latest, windows-latest ]
         experimental: [false]
+        include:
+          - { ruby: truffleruby-head, os: ubuntu-latest,  experimental: true }
     runs-on: ${{ matrix.os }}
     continue-on-error: ${{ matrix.experimental }}
     timeout-minutes: 15