Remove experimental rubies from ci run

Author: wildmaples

.github/workflows/ci.yml

@@ -4,18 +4,12 @@ on: [push, pull_request]
 jobs:
   build:
     runs-on: ubuntu-latest
-    continue-on-error: ${{ matrix.experimental }}
 
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.7, jruby, jruby-head, truffleruby-head]
+        ruby: [2.4, 2.5, 2.6, 2.7, 3.0, jruby, jruby-head]
         experimental: [false]
-        include:
-          - ruby: head
-            experimental: true
-          - ruby: truffleruby
-            experimental: true
 
     env:
       JAVA_OPTS: '-Xmx1024m'