Bug: The payment block introducer looks odd when only one block is available

### Impacted plugin

Jetpack

### Steps to Reproduce

1. Once #22491 is merged, or by following the steps there to set it up
2. On a free-tier wpcom connected Jetpack site
2. Create a new post
3. In the block inserter choose 'One payment' (or whatever it ends up being called)

### A clear and concise description of what you expected to happen.

Not sure! Maybe I shouldn't have been offered to use the 'One payment' block at all - but then that is confusing in of itself, maybe it should automatically choose the one option there is - but again that is confusing of itself.

### What actually happened

The payment block selector gives me a choice of one, which looks a bit odd

### Other information


Implementing #22582 would mean there's always a choice of at least two, and this issue would then not be reproducible

### Operating System

_No response_

### OS Version

_No response_

### Browser

Chrome/Chromium, Firefox, Microsoft Edge, Safari

### Browser Version(s)

_No response_

Start by reviewing the reproduction steps and the referenced issues #22491 and #22582, then reproduce the singleton choice in the WordPress block inserter on a free-tier connected Jetpack site. The issue needs an agreed interaction for when only one payment block is available; done means the inserter no longer presents a confusing one-item choice.

Written by the indexing model from the issue text.