When we downgrade, but on target php 8.1+, first class callable feature is already exists.
Function replacement usage should use code snippets, like in:
https://github.com/rectorphp/rector-downgrade-php/blob/73e0dbb5437d07df74b01773c6db92720fe485a9/rules/DowngradePhp72/Rector/FuncCall/DowngradeStreamIsattyRector.php#L148
then remove the firstClassCallable() check to avoid function not exists on downgraded code.
Because first class callable is available on php 8.1+, so skip isFirstClassCallable() will cause invalid change when code available to be downgraded.
see https://3v4l.org/6sLa4
to avoid error on first class callable, the args should be used instead:
-$args = $node->getArgs();
+$args = $node->args;