Add skip for 1946-asan + interp-ac

This combination is so slow the test won't finish in the 15 minute
timeout.

Test: SANITIZE_HOST=address ./test/testrunner/testrunner.py -b --host --interp-ac -t 1946
Change-Id: Idf17570aac82f0fcbbd10be03ee91223319878d7
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 15c1198..4bb5f07 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -548,6 +548,18 @@
         "bug": "b/33650497"
     },
     {
+        "tests": "1946-list-descriptors",
+        "description": "ASAN+interp-ac/switch interpreter means this is too slow to finish in the timeout",
+        "variant": "target & interp-ac",
+        "env_vars": {"SANITIZE_TARGET": "address"}
+    },
+    {
+        "tests": "1946-list-descriptors",
+        "description": "ASAN+interp-ac/switch interpreter means this is too slow to finish in the timeout",
+        "variant": "host & interp-ac",
+        "env_vars": {"SANITIZE_HOST": "address"}
+    },
+    {
         "tests": "202-thread-oome",
         "description": "ASAN aborts when large thread stacks are requested.",
         "variant": "host",