Allow cpy.Apply to not copy the tree

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/PCPCheckAndHeal.scala

@@ -124,7 +124,7 @@ class PCPCheckAndHeal(@constructorOnly ictx: Context) extends TreeMapWithStages(
       val targs2 = targs.map(targ => TypeTree(healTypeOfTerm(quote.fun.srcPos)(targ.tpe)))
       cpy.Apply(quote)(cpy.TypeApply(quote.fun)(fun, targs2), body2 :: Nil)
     else
-      val quotes = quote.args.map(transform)
+      val quotes = quote.args.mapConserve(transform)
       body.tpe match
         case tp @ TypeRef(x: TermRef, _) if tp.symbol == defn.QuotedType_splice =>
           // Optimization: `quoted.Type.of[x.Underlying](quotes)`  -->  `x`