fixup! Add test for more complex narrowing use case

Fix for more deterministic behaviour

Author: Don-Burns

mypy/checker.py

@@ -5512,7 +5512,7 @@ def visit_match_stmt(self, s: MatchStmt) -> None:
                 unmatched_types = else_map
 
             if unmatched_types is not None:
-                for typ in set(unmatched_types.values()):
+                for typ in list(unmatched_types.values()):
                     self.msg.match_statement_inexhaustive_match(typ, s)
 
             # This is needed due to a quirk in frame_context. Without it types will stay narrowed

test-data/unit/check-python310.test

@@ -2786,7 +2786,7 @@ class B(TypedDict):
     num: int
 
 d: A | B
-match d["tag"]: # E: Cases within match statement do not exhaustively handle all values: "B". If not intended to handle all cases, use `case _: pass` # E: Cases within match statement do not exhaustively handle all values: "Literal['b']". If not intended to handle all cases, use `case _: pass`
+match d["tag"]: # E: Cases within match statement do not exhaustively handle all values: "Literal['b']". If not intended to handle all cases, use `case _: pass` # E: Cases within match statement do not exhaustively handle all values: "B". If not intended to handle all cases, use `case _: pass`
     case "a":
         reveal_type(d)  # N: Revealed type is "TypedDict('__main__.A', {'tag': Literal['a'], 'name': builtins.str})"
         reveal_type(d["name"])  # N: Revealed type is "builtins.str"