Donations block: Button wording carries over to all three payment types once edited

By default, the Donations block provides distinct wording for each type of payment option: One-Time, Monthly, and Yearly. However, once the **button** text is edited in any of the three views, it persists across all three views and cannot be edited separately.

#### Steps to reproduce

1. Insert a donation block
2. Connect Stripe account
3. Click One-Time/Monthly/Yearly tabs at the top to see default button wording in each view:

##### One-Time Donation:


For one-time donations, the default button wording says "Donate"

##### Monthly Donation:


For monthly donations, the default button wording says "Donate Monthly"

##### Yearly Donation:


For yearly donations, the default button wording says "Donate Yearly"

4. In the One-Time panel view, change the default button wording from "Donate" to "Donate One Time."
5. Click the Monthly and Yearly panels to view the button wording there, which both now also say "Donate One Time."

#### What I expected

I should be able to modify the button wording separately for One-Time, Monthly, and Yearly options.

#### What happened instead

The moment the button wording is edited, it becomes tied together across all three payment options and cannot be edited separately, so the button says the same thing in every view.

#### Browser / OS version

n/a

#### Video


Screencast with audio: https://d.pr/v/5C5Gk5/vhrNbTQZeW

#### Context / Source

#dogfooding, #manual-testing

No user report

Start by reproducing the issue in the Donations block with a connected Stripe account, switching among the One-Time, Monthly, and Yearly tabs. Trace where the button wording is stored when one view is edited. Done means each payment type retains and displays its own button wording.

Written by the indexing model from the issue text.