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.

[Girgias]

I think the new wording makes more sense, as the current one is very confusing.

I was having a quick look to see why this error message appears, and it's due to the fact that the +/* ZPP specifiers (and the fast ZPP Z_PARAM_VARIADIC equivalent) don't support the named parameters. And it doesn't seem like it's very easy or even sensible to migrate to the Z_PARAM_VARIADIC_WITH_NAMED fast ZPP specifier that does support the named args.

[iluuu1994]

IMO this could still be slightly simplified. How about something like:

Suggested change

	array_merge() does not accept named arguments for variadic parameters
	Internal function array_merge() does not accept named variadic arguments

Meaning, any variadic argument must be positional, not named. Also hint at the fact that this is only the case for internal functions. @Girgias WDYT?

[Girgias]

I like this wording :)

[jorgsowa]

sure, changed 👍🏽