Fix Plugin Check Errors: MissingTranslatorsComment & MissingSingularPlaceholder

[masteradhoc]

Fixes #757

What?

This PR intends to fix the MissingTranslatorsComment & MissingSingularPlaceholder Errors shown by the Plugin Check Plugin

Why?

This PR is necessary to resolve WordPress Coding Standards (PHPCS) i18n errors related to translatable strings with placeholders.

How?

The PR addresses these issues by:

• Adding appropriate /* translators: ... */ comments immediately above all affected translation function calls that include placeholders, clarifying their meaning for translators.
• Updating the singular form of an _n() call to include the same placeholders as the plural form, ensuring placeholder parity as required by WordPress i18n guidelines.

Testing Instructions

1. Install Plugin Check Plugin
2. Choose Two Factor, Categories = "General" and Types = "Error" & "Warning"
3. see results
4. apply fix
5. see results

Screenshots or screencast

Changelog Entry

Fixed - Resolved WordPress i18n coding standards errors by adding missing translator comments and correcting placeholder usage in translatable strings.

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Co-authored-by: masteradhoc <masteradhoc@git.wordpress.org>
Co-authored-by: kasparsd <kasparsd@git.wordpress.org>

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[kasparsd]

Could you please update the associated test case?

Noting that we also have #437 for general PHPCS cleanup.

[kasparsd]

Looks like this requires updating the associated phpunit test case:

1. Test_ClassTwoFactorCore::test_maybe_show_last_login_failure_notice
   Failed asserting that '
   WARNING: Your account has attempted to login 1 time without providing a valid two factor token. The last failed login occurred 5 seconds ago. If this wasn't you, you should reset your password.
   ' contains "login without providing a valid two factor token".

/var/www/html/wp-content/plugins/two-factor/tests/class-two-factor-core.php:630

[masteradhoc]

@kasparsd thanks for the hint!