The “Would you mind telling us why you’re leaving?” form can be submitted without checking an option

[mariaberlinger]

FxA version:

• 1.239.0;

Prerequisites:

• Be localized in US;
• Have an fxa account;

Steps to reproduce:

1. Navigate to https://accounts.stage.mozaws.net/ and login using an existing account;
2. Click on the "Email communications" option displayed in the navigation menu;
3. Click on "Sign in" button;
4. Check the "Remove me from all the subscriptions on this page:" checkbox displayed at the bottom of the page and click the Save Preferences button;
5. Do not check the checkbox which describe your unsubscribing reason and click "Submit" button;

Expected result:

• The Submit button is not available or is disabled;

Actual result:

• The submit button can be clicked without any issue;