Add test gcstress 968 to knownfailures.json

This test was occasionally timing out.

Test: ./test.py --host --gcstress -j40
Change-Id: Ib69088f67d72bc72f642c2155c67f48b7e4f2a68
diff --git a/test/knownfailures.json b/test/knownfailures.json
index f7fb357..d8e01a7 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -108,20 +108,19 @@
                         "non-deterministic. Same for 913."]
     },
     {
-        "tests": "961-default-iface-resolution-gen",
+        "tests": ["961-default-iface-resolution-gen",
+                  "964-default-iface-init-gen",
+                  "968-default-partial-compile-gen"],
         "variant": "gcstress",
-        "description": ["961-default-iface-resolution-gen and",
-                        "964-default-iface-init-genare very long tests that",
+        "description": ["961-default-iface-resolution-gen,",
+                        "968-default-partial-compile-gen and",
+                        "964-default-iface-init-gen are very long tests that",
                         "often will take more than the timeout to run when",
                         "gcstress is enabled. This is because gcstress slows",
                         "down allocations significantly which these tests do a",
                         "lot."]
     },
     {
-        "tests": "964-default-iface-init-gen",
-        "variant": "gcstress"
-    },
-    {
         "tests": "154-gc-loop",
         "variant": "gcstress | jit & debug",
         "description": ["154-gc-loop depends GC not happening too often"],