Fix warning about deprecated ability

[Camwyn]

see #2333

🎫 Ticket

TEC-5086

🗒️ Description

As explained by one of our users here, our Tribe__PUE__Checker::get_installed_version() function was returning null because it was looking for event-aggregator/event-aggregator.php. EA is not standalone plugin, it comes bundled with TEC. Passing null to version_compare() in PHP >8.1 caused this warning:

Deprecated: version_compare(): Passing null to parameter #2 ($version2) of type string is deprecated in ..\the-events-calendar\common\src\Tribe\PUE\Checker.php on line 1710

The fix is to pass an empty string in this case.

🎥 Artifacts

✔️ Checklist

• Ran npm run changelog to add changelog file(s). More info here
• Code is covered by NEW wpunit or integration tests.
• Code is covered by EXISTING wpunit or integration tests.
• Are all the required tests passing?
• Automated code review comments are addressed.
• Have you added Artifacts?
• Check the base branch for your PR.
• Add your PR to the project board for the release.

[codingmusician]

Code is approved, although there are tests failing...