Bump integration test's timeout on CI to 30s (#1122)

This is to allow ZJIT test against bundled gems on CI.

I don't see the same error locally so I'm not touching the default timeout yet.

Author: st0012

test/irb/helper.rb

@@ -114,7 +114,7 @@ def execute_lines(*lines, conf: {}, main: self, irb_path: nil)
 
   class IntegrationTestCase < TestCase
     LIB = File.expand_path("../../lib", __dir__)
-    TIMEOUT_SEC = 3
+    TIMEOUT_SEC = ENV["CI"] ? 30 : 3
 
     def setup
       @envs = {}