Bug Report

Minimal PHP Code Causing Issue

join(['a'], "string");

https://getrector.com/demo/19b79beb-de09-488e-8a60-5ec82d8a9cdf

Expected Behaviour

join("string",['a']);

Either the rector should take the alias 'join' into account, OR the php80.php should do as first line:
$rectorConfig->ruleWithConfiguration(RenameFunctionRector::class, ['join' => 'implode']);