Re-enable Truffleruby on the CI (#698)

Re-enable truffleruby on the CI

Author: anakinj

.github/workflows/test.yml

@@ -47,11 +47,10 @@ jobs:
             ruby: "2.5"
             gemfile: gemfiles/openssl.gemfile
             experimental: false
-          # Disable temporarily due to `ArgumentError: circular causes` error
-          # - os: ubuntu-latest
-          #   ruby: "truffleruby-head"
-          #   gemfile: "gemfiles/standalone.gemfile"
-          #   experimental: true
+          - os: ubuntu-latest
+            ruby: "truffleruby-head"
+            gemfile: "gemfiles/standalone.gemfile"
+            experimental: true
           - os: ubuntu-latest
             ruby: head
             gemfile: gemfiles/standalone.gemfile