Scaladoc doesn't generate `abstract override` modifier for mixins

[hamzaremmal]

Compiler version

3.6.3

Minimized code

I'm pointing to the only abstract override in the scala2 part of the stdlib: https://www.scala-lang.org/api/3.6.3/scala/collection/BitSetOps.html#diff-703

Otherwise, this might be a minimisation:

trait Foo:
  def foo: Int

trait IncFoo extends Foo:
  abstract override def foo: Int = super.foo + 1

Expectation

Scaladoc should be add the abstract override modifier for mixins.