Fix typo in modified (commented-out) code

Author: Blaisorblade

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

@@ -1614,7 +1614,7 @@ class RefChecks extends MiniPhase { thisPhase =>
       } catch {
         case ex: TypeError =>
           if (settings.debug) ex.printStackTrace()
-          unit.error(tree.pos, ex.toMssage)
+          unit.error(tree.pos, ex.toMessage)
           tree
       } finally {
         localTyper = savedLocalTyper