Disable autocomplete for captcha inputs

[denistrator]

Description

This PR removes captcha input autocomplete

Manual testing scenarios

1. Go to login page
2. Try to login with incorrect login/password until you get captha
3. Click on captcha input field

Before

After

[magento-engcom-team]

Hi @denistrator. 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:

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[magento-engcom-team]

Hi @denistrator. Thank you for your contribution.
We will aim to release these changes as part of 2.2.6.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.