Fix implicit scope liftToAnchors for parameter lower bounds

Related to #23672 (comment)
But we were dropping a lower bound in this case.

[Cherry-picked 6732630]

Author: EugeneFlesselle

compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -832,7 +832,7 @@ trait ImplicitRunInfo:
               WildcardType
             else
               seen += t
-              t.superType match
+              t.underlying match
                 case TypeBounds(lo, hi) =>
                   if lo.isBottomTypeAfterErasure then apply(hi)
                   else AndType.make(apply(lo), apply(hi))

tests/pos/i21951b.scala

@@ -0,0 +1,12 @@
+
+class A
+object A:
+  given A = ???
+
+class B[X]
+object B:
+  given g[T]: B[T] = ???
+
+object Test:
+  def foo[X >: A] = summon[X] // was error
+  def bar[F[T] >: B[T]] = summon[F[Int]] // was error