[Forwardport] Fix "Confirmation request" email is sent on customer's newsletter unsubscribe action

[ihor-sviziev]

Original Pull Request

#15464

Description

This fix related to #15218
Skip update customer subscribe status from save subscribe action from my account when nothing is changed.

Fixed Issues (if relevant)

1. Skip update customer subscribe status from save subscribe action from my account when nothing is changed.

Manual testing scenarios

1. Activate "Need to Confirm" for the newsletter subscription
2. Register a new customer
3. Subscribe to the newsletter
4. Confirm the newsletter subscription.
5. Login as created customer
6. Unsubscribe from the newsletter from the customer area

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @ihor-sviziev. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[magento-engcom-team]

Hi @ihor-sviziev. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.