Improve url validation to check duplicate protocol

[nikunj8866]

Improved is_valid_url() to detect duplicated protocol in URLs.

This PR enhances the is_valid_url() function to identify and reject URLs that contain duplicated protocols (e.g., https://http://example.com/).

Fixes #890

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[nikunj8866]

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: nikunj8866 <nikunj8866@git.wordpress.org>
Co-authored-by: ernilambar <rabmalin@git.wordpress.org>

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[ernilambar]

@nikunj8866 Thanks for the PR. Can you please add PHP Unit test also?