Temporary work-around: Do not test for bad source

In production this returns a 403 instead of a 504, because we call the
MW API end point regardless of the wiki domain we are after, while
outside of production we use the wiki's domain directly in the URI.
Therefore, we cannot set a unique status code, so disable this specific
check for now.

Bug: T165760
Change-Id: I979211772161190904289a1766616b674cff58cf