Only check for Scala2LocalSuffix in methods on Scala2x classes

fixes lampepfl#15943

Author: KacperFKorban

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -768,7 +768,7 @@ object SymDenotations {
 
     /** Is this a getter? */
     final def isGetter(using Context): Boolean =
-      this.is(Accessor) && !originalName.isSetterName && !originalName.isScala2LocalSuffix
+      this.is(Accessor) && !originalName.isSetterName && !(originalName.isScala2LocalSuffix && symbol.owner.is(Scala2x))
 
     /** Is this a setter? */
     final def isSetter(using Context): Boolean =

tests/run/i15943.check

@@ -0,0 +1 @@
+asdf

tests/run/i15943.scala

@@ -0,0 +1,7 @@
+case class A(`a `: String)
+
+@main
+def Test = {
+  val a = A("asdf")
+  println(a.`a `)
+}