Fix #5463: Replace the call to the String#lines method

Author: Glavo

compiler/src/dotty/tools/dotc/util/ParsedComment.scala

@@ -8,6 +8,7 @@ import dotty.tools.dotc.printing.SyntaxHighlighting
 
 import scala.Console.{BOLD, RESET, UNDERLINED}
 import scala.collection.immutable.ListMap
+import scala.collection.immutable.StringOps
 import scala.util.matching.Regex
 
 /**
@@ -148,7 +149,7 @@ object ParsedComment {
    * @return The list of items, in markdown.
    */
   private def toMarkdownList(ctx: Context, items: List[String]): String = {
-    val formattedItems = items.map(_.lines.mkString(System.lineSeparator + "   "))
+    val formattedItems = items.map(s => new StringOps(s).lines.mkString(System.lineSeparator + "   "))
     formattedItems.mkString(" - ", System.lineSeparator + " - ", "")
   }