Disable voting for mwext-ImageMetrics-qunit

The job never worked and prevent patches from landing in.  Dies with a
cryptic error:

  JQMIGRATE: Logging is active
  Exception thrown by test.module1
  Error: expected Error: expected

Bug: 71782
Change-Id: I6d25211f81086f6e1dfadca92ecc239e99b2f521