Bug 1106776: update test results now that they are consistent. r=karlt

When a subtest times out, it causes the parent to time out as well.

testing/web-platform/meta/media-source/mediasource-config-change-mp4-a-bitrate.html.ini

@@ -1,4 +1,11 @@
 [mediasource-config-change-mp4-a-bitrate.html]
   type: testharness
+  disabled:
+    if (os == "win") and (version != "5.1.2600"): occasional timeout
   [Tests mp4 audio-only bitrate changes.]
-    disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1106776
+    disabled:
+      if (os == "win") and (version != "5.1.2600"): occasional timeout.
+    expected:
+      if os == "mac": PASS
+      FAIL
+