Added Unit Test for WindowsSmtpConfig Plugin

[vasilii-b]

Description

This PR cover Magento\Email\Test\Unit\Model\Plugin\WindowsSmtpConfig plugin with unit test.

Fixed Issues (if relevant)

N/A

Manual testing scenarios

N/A

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 @vasilii-b. Thank you for your contribution
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[rogyar]

Please, declare the strict types.

[rogyar]

It does not look like a "mock". We test the real object. Please, fix the naming.

[rogyar]

Hello @vasilii-b. Thank you for your contribution. Please, consider fixing a few minor issues mentioned in the review

[vasilii-b]

Thank you @rogyar, will do.

[vasilii-b]

Hi @rogyar , I have added requested changes, but I see the Codacy failed with a strange issue. Could you please have a look and advice what to do there ? 🤔 Thank you!

[rogyar]

I've double checked the result and see no issue. So, no worries

[magento-engcom-team]

Hi @rogyar, thank you for the review.
ENGCOM-3234 has been created to process this Pull Request

[magento-engcom-team]

Hi @vasilii-b. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.