Deprecation Warnings in Backup Logs with PHP 8.1+

[saranshj4]

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Describe the bug
When running backups (both manual and scheduled) with BackWPUp on PHP 8.1+ and WordPress 6.6.2, users are encountering thousands of deprecation warnings. The errors mainly involve passing null to parameters that expect a string or array input. Examples include warnings from strlen() and preg_replace(). These notices clutter the logs with thousands of lines, impacting usability.

Acceptance Criteria (for WP Media team use only)
Clear instructions for developers, to be added before the grooming

[saranshj4]

https://wordpress.org/support/topic/passing-null-to-parameter-errors-php-8-2-20/
https://wordpress.org/support/topic/deprecation-warnings-in-log/
https://wordpress.org/support/topic/error-after-upgrading-to-php-8-2/

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