[Ignition] Skip another failing mjsunittest on ignition.

Skips regress-446389.

BUG=v8:4280
LOG=N
NOTRY=true
TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/1412313010

Cr-Commit-Position: refs/heads/master@{#31891}

test/mjsunit/mjsunit.status

@@ -886,6 +886,7 @@
   'regress/regress-4374': [SKIP],
   'regress/regress-4388': [SKIP],
   'regress/regress-444805': [SKIP],
+  'regress/regress-446389': [SKIP],
   'regress/regress-4515': [SKIP],
   'regress/regress-4521': [SKIP],
   'regress/regress-4525': [SKIP],