Bug 1362165: P12. Updated wpt expectation. r=gerald

New test will error until bug 1367993 is fixed.

MozReview-Commit-ID: KgyquX6klE8

--HG--
extra : rebase_source : 648acc98a863ed99f60ad2e5a88076b1676f4247

testing/web-platform/meta/media-source/mediasource-append-buffer.html.ini

@@ -0,0 +1,4 @@
+[mediasource-append-buffer.html]
+  type: testharness
+  expected: ERROR
+