YARN-11790. TestAmFilter#testProxyUpdate fails in some networks (#7478) Contributed by Chris Nauroth.

Reviewed-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: Shilun Fan <slfan1989@apache.org>

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/test/java/org/apache/hadoop/yarn/server/webproxy/amfilter/TestAmFilter.java

@@ -202,7 +202,7 @@ public class TestAmFilter {
 
     // change proxy configurations
     params = new HashMap<>();
-    params.put(AmIpFilter.PROXY_HOSTS, "unknownhost");
+    params.put(AmIpFilter.PROXY_HOSTS, "unknownhostaf79d34c");
     params.put(AmIpFilter.PROXY_URI_BASES, proxyUri);
     conf = new DummyFilterConfig(params);
     filter.init(conf);