[Donation page] Verify if a user can make a payment with entered valid specified sum

**Priority:**
High

**Preconditions**
1. Click on the Burger menu in the right upper corner of the site.
2. Click on the 'Донати'.

**Steps to reproduce**
1. Enter the specified sum in the 'Ввести суму' field (e.g. 2000₴).
2. Click on the 'Я даю згоду на обробку моїх персональних даних' button.
3. Click on the 'Підтримати' button.

**Expected result**
The user is redirected to the monobank payment page in the new window.

**User story:**
#911

Start at the donation page through the Burger menu and exercise the specified-sum flow: enter 2000₴, give consent, and click “Підтримати.” Verify whether the user is redirected to the Monobank payment page in a new window; done means this expected result works reliably for a valid entered sum.

Written by the indexing model from the issue text.