Use List.fill instead of range [ci: last-only]

[som-snytt]

Follow-up to 8c00042

Noticed during scala/scala3#15144 at https://github.com/scala/scala3/blob/main/compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala#L383 where it induced an explanatory comment.

[lrytz]

hmm, do we have a new unstable test? :-/ it was added recently in #11024

!!  1 - presentation/dollar-completion            [output differs]
% diff /home/runner/work/scala/scala/test/files/presentation/dollar-completion.check /home/runner/work/scala/scala/test/files/presentation/dollar-completion-presentation.log
@@ -3,22 +3,14 @@ reload: Completions.scala
 askScopeCompletion at Completions.scala(5,2)
 ================================================================================
 [response] askScopeCompletion at (5,2)
-retrieved 16 members
+retrieved 8 members
 abstract trait T extends AnyRef
 case class C1 extends Product with Serializable
 class C2 extends AnyRef
 def <init>(x: Int): test.C1
-def canEqual(x$1: Any): Boolean
 def copy(x: Int): test.C1
-def productArity: Int
-def productElement(x$1: Int): Any
 object C1
-override def equals(x$1: Any): Boolean
-override def hashCode(): Int
-override def productElementName(x$1: Int): String
-override def productIterator: Iterator[Any]
 override def productPrefix: String
-override def toString(): String
 private[this] val x: Int
 ================================================================================

[som-snytt]

hmm, indeed. I don't remember what my second thoughts were on #10867 to fix something about PC tests.