ProblemList java/lang/invoke/lambda/LambdaFileEncodingSerialization.java on linux-x64

There are currently 34 sightings of this test failure since I filed
the bug on 2020.07.08. I think it is time to ProblemList this test. For
whatever reason, this failures only seems to be happening on Linux-X64
machines.

Here's the context diffs:

$ hg diff
diff -r d62da6fc4074 test/jdk/ProblemList.txt
--- a/test/jdk/ProblemList.txt Thu Jul 23 20:25:41 2020 +0100
+++ b/test/jdk/ProblemList.txt Thu Jul 23 16:20:37 2020 -0400
@@ -571,6 +571,7 @@
 java/lang/ProcessHandle/InfoTest.java 8211847 aix-ppc64
 java/lang/invoke/LFCaching/LFMultiThreadCachingTest.java 8151492 generic-all
 java/lang/invoke/LFCaching/LFGarbageCollectedTest.java 8078602 generic-all
+java/lang/invoke/lambda/LambdaFileEncodingSerialization.java 8249079 linux-x64
 
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