test: mark test-child-process-exit-code flaky

Refs: # #25033

PR-URL: #25050
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Gireesh Punathil <[email protected]>

Author: Trott

test/parallel/parallel.status

@@ -7,6 +7,8 @@ prefix parallel
 [true] # This section applies to all platforms
 # https://github.com/nodejs/node/issues/23207
 test-net-connect-options-port: PASS,FLAKY
+# https://github.com/nodejs/node/issues/25033
+test-child-process-exit-code: PASS,FLAKY
 
 [$system==win32]
 test-http2-pipe: PASS,FLAKY