Add 968 to skips for jvmti-stress

This test can take too long on the buildbots and cause timeouts.

Test: None
Change-Id: Ibce2c4e449acc246529d51fbd87508d57622377c
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 9db8e9d..b38f914 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -412,7 +412,8 @@
     {
         "tests": [
             "961-default-iface-resolution-gen",
-            "964-default-iface-init-gen"
+            "964-default-iface-init-gen",
+            "968-default-partial-compile-gen"
         ],
         "description": ["Tests that just take too long with jvmti-stress"],
         "variant": "jvmti-stress | redefine-stress | trace-stress | step-stress"