chore: improve errror message when passing named parameter for variadic

[jorgsowa]

I was a bit confused when I encountered the error does not accept unknown named parameters.
The issue was that I passed an associative array to a variadic parameter, which made the message misleading.
Because of that, I felt a clearer error message would be more appropriate in this case.

I changed the error message from <function> does not accept unknown named parameters to <function> does not accept named arguments for variadic parameters.

The discussion about this problem was touched in #11026

[iluuu1994]

/cc @Girgias @kocsismate, given you have both worked on error messages historically.