[macos] test javax/swing/dnd/8139050/NativeErrorsInTableDnD.java does not cleanup

javax/swing/dnd/8139050/NativeErrorsInTableDnD.java times out
as it apparently does not clean up a forked process.
This happens even in a jtreg run of just this one test.
Here is part of the stack dump

"MainThread" #13 prio=5 os_prio=31 tid=0x00007f8229883000 nid=0x6903 runnable [0x000070000a982000]
   java.lang.Thread.State: RUNNABLE
at java.io.FileInputStream.readBytes(java.base/Native Method)
at java.io.FileInputStream.read(java.base/FileInputStream.java:279)
at java.io.BufferedInputStream.read1(java.base/BufferedInputStream.java:290)
at java.io.BufferedInputStream.read(java.base/BufferedInputStream.java:351)
- locked <0x000000070f69a1b0> (a java.lang.ProcessImpl$ProcessPipeInputStream)
at sun.nio.cs.StreamDecoder.readBytes(java.base/StreamDecoder.java:284)
at sun.nio.cs.StreamDecoder.implRead(java.base/StreamDecoder.java:326)
at sun.nio.cs.StreamDecoder.read(java.base/StreamDecoder.java:178)
- locked <0x000000070f6ab3d0> (a java.io.InputStreamReader)
at java.io.InputStreamReader.read(java.base/InputStreamReader.java:185)
at java.io.BufferedReader.fill(java.base/BufferedReader.java:161)
at java.io.BufferedReader.readLine(java.base/BufferedReader.java:326)
- locked <0x000000070f6ab3d0> (a java.io.InputStreamReader)
at java.io.BufferedReader.readLine(java.base/BufferedReader.java:392)
at NativeErrorsInTableDnD.doExec(NativeErrorsInTableDnD.java:124)
at NativeErrorsInTableDnD.createChildProcess(NativeErrorsInTableDnD.java:105)
at NativeErrorsInTableDnD.main(NativeErrorsInTableDnD.java:57)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(java.base/Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(java.base/NativeMethodAccessorImpl.java:62)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(java.base/DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(java.base/Method.java:569)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:115)
at java.lang.Thread.run(java.base/Thread.java:832)

"process reaper" #14 daemon prio=10 os_prio=31 tid=0x00007f82298f5000 nid=0x6c03 runnable [0x000070000a9aa000]
   java.lang.Thread.State: RUNNABLE
at java.lang.ProcessHandleImpl.waitForProcessExit0(java.base/Native Method)
at java.lang.ProcessHandleImpl.access$000(java.base/ProcessHandleImpl.java:50)
at java.lang.ProcessHandleImpl$1.run(java.base/ProcessHandleImpl.java:138)
at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base/ThreadPoolExecutor.java:1128)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base/ThreadPoolExecutor.java:628)
at java.lang.Thread.run(java.base/Thread.java:832)