Add 1946 to gcverify and trace known failures

This test does a lot of calls. This causes it to often timeout on
gcverify or trace.

Test: None
Change-Id: Ic5ee5f48cd0b9ca237f353b451cabf6cbb24b826
diff --git a/test/knownfailures.json b/test/knownfailures.json
index ddf9098..fe1e31e 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -122,6 +122,11 @@
                         "non-deterministic. Same for 913."]
     },
     {
+        "tests": ["1946-list-descriptors"],
+        "variant": "gcverify | trace",
+        "description": "This test is rather slow and gcverify or trace often cause it to timeout."
+    },
+    {
         "tests": ["961-default-iface-resolution-gen",
                   "964-default-iface-init-gen",
                   "968-default-partial-compile-gen"],