Try to fix spurious unreachability warnings

Author: A5rocks

mypy/checkexpr.py

@@ -5495,7 +5495,8 @@ def visit_lambda_expr(self, e: LambdaExpr) -> Type:
                 # Lambdas can have more than one element in body,
                 # when we add "fictional" AssignmentStatement nodes, like in:
                 # `lambda (a, b): a`
-                self.chk.accept(e.body)
+                with self.chk.binder.frame_context(can_skip=True, fall_through=0):
+                    self.chk.accept(e.body)
 
                 # Only type check the return expression, not the return statement.
                 # There's no useful type context.