Add jruby-head and disable allow-failure

In order to help ensure JRuby does not break mustermann again,
remove the allow-failure flag and add jruby-head with sinatra head
for more coverage.

The issue reported in jruby/jruby#8920 wouldn't have been released
if it had been caught by jruby-head testing in mustermann, and
having allow-failure means bugs introduced by JRuby may never be
caught by mustermann CI.

I will push additional fixes to get the remaining failure green.

Author: headius

.github/workflows/test.yml

@@ -29,8 +29,8 @@ jobs:
           - { ruby: 2.6, sinatra: ~> 3.0.0 }
           - { ruby: 3.4, sinatra: head }
           - { ruby: head, sinatra: head }
-          # https://github.com/sinatra/mustermann/issues/72
-          - { ruby: jruby, sinatra: ~> 4.0.0, allow-failure: true }
+          - { ruby: jruby, sinatra: ~> 4.0.0 }
+          - { ruby: jruby-head, sinatra: head }
           # https://github.com/sinatra/mustermann/issues/143
           - { ruby: truffleruby, sinatra: ~> 4.0.0, allow-failure: true }
     env: