Add failing test for filtering a Count annotation

After annotating and filtering a queryset for the number of m2m related
objects, subsequent filters using __in falsely return an empty result.

Example
-------
book = Book.objects.all()[0]
author1 = book.authors.all()[0]
author2 = book.authors.all()[1]

annotated_query = Book.objects.annotate(c=Count('authors')).filter(c=2)
query = annotated_query.filter(authors__in=[author1, author2])