Parallel Gateway continues if multiple tokens are received on the same path

**Describe the bug**
I have a process with a parallel gateway that waits on two branches, one of which has a loop which checks every hour whether a variable is true.
I would expect that the gateway waits for both branches to complete before proceeding, but it actually proceeds if the same branch completes twice.

This can happen because a Message Catch Event can spawn a new token, which gets sent down the same branch again.

**Expected behavior**
I would expect the parallel gateway to wait for a token from each branch to arrive, rather than just waiting for 2 tokens to arrive from the same branch.

まず、説明されているプロセスを再現します。2つの分岐を持つ parallel gateway に、ループと、1つの分岐に沿って複数のトークンを送信できる Message Catch Event を含めます。gateway が入力トークンをどのようにカウントし、分岐を区別しているかを追跡します。片方の分岐が複数のトークンを受け取る場合も含め、gateway が各分岐から1つずつトークンを受け取った後にのみ進むことを確認できれば完了です。

索引モデルが issue の本文から書いたものです。