Test only with truffleruby-head

The old version is already known to fail.

.github/workflows/test.yml

@@ -8,6 +8,7 @@ permissions:  # added using https://github.com/step-security/secure-workflows
 jobs:
   ruby-versions:
     uses: ruby/actions/.github/workflows/ruby_versions.yml@master
+    engine: cruby-jruby
 
   test:
     needs: ruby-versions
@@ -16,11 +17,12 @@ jobs:
       matrix:
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
         os: [ubuntu-latest, macos-latest, windows-latest]
-        exclude:
-          - os: windows-latest
-            ruby: truffleruby
-          - os: windows-latest
+        include:
+          - os: ubuntu-latest
             ruby: truffleruby-head
+          - os: macos-latest
+            ruby: truffleruby-head
+        exclude:
           - os: windows-latest
             ruby: jruby
           - os: windows-latest
@@ -43,7 +45,6 @@ jobs:
       run: bundle exec rake
       env:
         RUBYOPT: --enable-frozen_string_literal
-      continue-on-error: ${{ startsWith(matrix.ruby, 'truffle') }}
     - if: ${{ matrix.ruby == 'head' && startsWith(matrix.os, 'ubuntu') }}
       run: bundle exec rake rdoc
     - if: ${{ matrix.ruby == 'head' && startsWith(matrix.os, 'ubuntu') }}