Missing unreachable match warning with only two cases

[bishabosha]

Compiler version

3.0.0

Minimized code

package akka.event

sealed trait LogEvent

object LogEvent:
  def myOrdinal(e: LogEvent): Int = e match
    case e: Error => 0
    // case e: Warning => 1
    case e: LogEventWithMarker => 2


case class Error() extends LogEvent
class Error2() extends Error() with LogEventWithMarker

// case class Warning() extends LogEvent

sealed trait LogEventWithMarker extends LogEvent

Output

compiles fine

Expectation

there should be an unreachable warning for case e: LogEventWithMarker, as which happens when we add another child to LogEvent (uncomment the lines in the example)

[liufengyun]

Fixed as part of #12549