Check valid WP version for Requires at least plugin header

[ernilambar]

Fixes #851

• Check added for Requires at least plugin header for validity of WordPress version
• Version check logic is similar to Tested up to.
• At 6.7 WP version, error will be generated for more than or equal to WP 6.9
• Unit tests added for the updated check

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: ernilambar <rabmalin@git.wordpress.org>
Co-authored-by: swissspidy <swissspidy@git.wordpress.org>
Co-authored-by: davidperezgar <davidperez@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.