Don't CI on ruby-head because of net-http-persistent.

Author: gkellogg

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
           - 2.5
           - 2.6
           - 2.7
-          - ruby-head
+          # - ruby-head # net-http-persistent
           - jruby
     steps:
       - name: Clone repository