Mark 719-varhandle-concurrency as known-failure

Temporary measure while we consider reducing the resource requirements
for this test.

Bug: 229958698
Test: art/test.py --host
Change-Id: Ie4f11f53b8b3fb1507bf7dc0a2dae018f48aa573
diff --git a/test/knownfailures.json b/test/knownfailures.json
index c258f0f..8b18d17 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -1498,5 +1498,10 @@
         "variant": "target & ndebug & 64",
         "bug": "b/224733324",
         "description": ["segfault in VarHandle::GetMethodTypeMatchForAccessMode"]
+    },
+    {
+        "tests": ["719-varhandle-concurrency"],
+        "bug": "b/229958698",
+        "description": ["SIGSEGV in pthread_create"]
     }
 ]