Move jruby-head to the experimental workflow

Author: eregon

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.4, 2.5, 2.6, 2.7, '3.0', 3.1, jruby, jruby-head]
+        ruby: [2.4, 2.5, 2.6, 2.7, '3.0', 3.1, jruby]
 
     env:
       JAVA_OPTS: '-Xmx1024m'

.github/workflows/experimental.yml

@@ -10,7 +10,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby: [head, truffleruby, truffleruby-head]
+        ruby: [head, jruby-head, truffleruby, truffleruby-head]
 
     env:
       JAVA_OPTS: '-Xmx1024m'