fix(child_process): fix inverted break condition in close method

In the close method's wait-for-exit loop, the condition
'break if living_process_exist' was inverted. It should be
'break unless living_process_exist'.

The current code breaks out of the loop as soon as it finds living
processes, skipping the wait for them to actually terminate. This
allows child processes to become orphaned or zombie processes during
shutdown, leaking resources held by those processes.

The shutdown method at line 142 correctly implements this pattern:
'if process_exists: sleep; else: break'.

Signed-off-by: Akanksha Trehun <akankshatrehun@gmail.com>

Author: magic-peach

lib/fluent/plugin_helper/child_process.rb

@@ -191,7 +191,7 @@ def close
             child_process_kill(process_info, force: true)
           end
 
-          break if living_process_exist
+          break unless living_process_exist
 
           sleep CHILD_PROCESS_LOOP_CHECK_INTERVAL
         end