https://codesearch.wmflabs.org/search/?q=5%5C.3&i=nope&files=%5C.php%24&repos= lists some back-compatible code that was written for the PHP 5.3 era.
This is no longer needed because all MediaWiki versions that are nowadays supported require at least PHP version 7.
Go through that output, find two specific instances of such code, and clean them up in a patch!
Example: https://gerrit.wikimedia.org/r/c/mediawiki/core/+/457812
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