resourceloader: Restrict addModuleStyles() to type=styles modules

resourceloader: Restrict addModuleStyles() to type=styles modules

If a type=general module is enqueued, don't try to load it as a
stylesheet.

* Per a464d1d41d69f12fe, state tracking is already disabled for
  these loads (as otherwise we wrongly claim state=ready, when in
  fact only the styles and not the scripts were loaded).

* The warning was added in a464d1d41d69f12fe.

* Default install (tested in Vagrant), Wikimedia Beta cluster, and
  Wikimedia production have seen zero violations of this warning
  in the past 7 days.

Raise severity to ERROR and add the 'continue' statement so that
these are now not loaded at all.

Bug: T92459
Change-Id: I211d56ac2df479ebf5b98667c613ecf81489539b