False-positive unreachable warning for a match using local object

[WojciechMazur]

Based on false-positive warning found in apache/pekko#1398

Compiler version

Last good release: 3.4.0-RC1-bin-20230901-89e8dba-NIGHTLY
First bad release: 3.4.0-RC1-bin-20230904-6dc3737-NIGHTLY
The first bad commit could be any of:
cae6786
4421d12

Affects 3.3.4-RC1 - the PR introducing regression was backported before detecting regression

Minimized code

def Test[U, A](thisElem: A, thatElem: U) = {
  case object passedEnd
  val any: Seq[Any] = ???
  any.zip(any)
    .map {
      case (`passedEnd`, r: U @unchecked) => (thisElem, r)
      case (l: A @unchecked, `passedEnd`) => (l, thatElem)
      case t: (A, U) @unchecked           => t // false-positive warning
    }
}

Output

-- [E030] Match case Unreachable Warning: /Users/wmazur/projects/sandbox/src/main/scala/test.scala:68:11 
68 |      case t: (A, U) @unchecked           => t
   |           ^^^^^^^^^^^^^^^^^^^^
   |           Unreachable case

Expectation

It should not warn for the 3rd case in the map function. This case is easily reachable.