[GR-66535] Unclosed external engine prevents host app termination.

PullRequest: graal/21256

Author: tzezula

sdk/src/org.graalvm.nativebridge/src/org/graalvm/nativebridge/ProcessIsolateThreadSupport.java

@@ -179,6 +179,7 @@ Future<Boolean> connectInBackgroundThread() {
             }
         });
         thread.setName(String.format("%s Connection Listen Thread", ProcessIsolateThreadSupport.class.getSimpleName()));
+        thread.setDaemon(true);
         thread.start();
         return result;
     }