[Bug]: Posting multiple upcoming transactions for the same schedule within the same upcoming periods uses the first upcoming date

### Verified issue does not already exist?

- [x] I have searched and found no existing issue

### What happened?

When using the Schedule feature, the user cannot post a future transaction. For example, if the user has multiple transaction upcoming in the schedule, regardless if the next calendar one is posted, any attempts to post the transaction for a scheduled component before then will result in the first upcoming transaction being posted.

Example, Weekly scheduled payment occurs to give 100 into an account:
If the user's upcoming transaction is scheduled for DAY+2, DAY+9, DAY+16 (doable if we set "upcoming" period to be 1 month), then posting any of those transaction (+2, +9, or +16) will result in the transaction being posted for DAY+2, regardless if DAY+2 was already posted or not.

### How can we reproduce the issue?

Define a transaction to occur weekly

Change the period so that multiple schedule payments occur

Starting page for transaction. Home Depot is due today (11/25/2025).

Post today (11/25/2025)'s due transaction.

It posted! Now, go to post the next upcoming transaction (12/02/2025)

Now there are two entries for 11/25/2025 and the upcoming transaction is still there, even though we posted it for (12/02/2025).

### Where are you hosting Actual?

None

### What browsers are you seeing the problem on?

_No response_

### Operating System

None