Syntax error when putting `def` in enum object after simple `case`

This doesn't compile:
```scala
enum class Ducks

object Ducks {
  case Dewey

  def wooohoo: Int = 1
}
```
```scala
-- [E039] Syntax Error: enumo.scala:6:6 ------------------------------------
6 |  def woohoo: Int = 1
  |      ^^^^^^
  |      ';' expected, but identifier found
```
This can be worked around by writing `case Dewey;` or `case Dewey extends Ducks`.