Skip splice level checking for <refinement> symbols

[jchyb]

This is safe to skip because symbols can only be a part of type refinement self referencing prefix, where it is impossible to splice anything.

For some context, this is how the test case looks in typer:

{
  final class $anon() extends AnyRef() {
    type T = Unit
    def make: T = ()
    def take(t: T): Unit = ()
  }
  new $anon():
    {z1 => Object{type T; def make: z1.T; def take(t: z1.T): Unit}}
}:
  Object
    {
      type T >: Nothing <: Any
      def make: <refinement>.this.T
      def take(t: <refinement>.this.T): Unit
    }

The compiler sometimes instead of creating a recursive type directly ({z1 => ...}), creates symbols which reference an enclosing refinement, replacing those with recursive types later.
Fixes #22648