[1.9.x] Forwardported 1.8.6 release note.

* Fixed system check crash on ``ForeignKey`` to abstract model

  (:ticket:`25503`).

* Fixed incorrect queries when you have multiple ``ManyToManyField``\s on

  different models that have the same field name, point to the same model, and

  have their reverse relations disabled (:ticket:`25545`).

* Allowed filtering over a ``RawSQL`` annotation (:ticket:`25506`).