Mark spl_autoload_register function arg as UNKNOWN

Not passing any parameters to this function has magic behavior.

Author: nikic

ext/spl/php_spl.stub.php

@@ -15,7 +15,7 @@ function spl_autoload_extensions(string $file_extensions = UNKNOWN): string {}
 
 function spl_autoload_functions(): array|false {}
 
-function spl_autoload_register($autoload_function = null, bool $throw = true, bool $prepend = false): bool {}
+function spl_autoload_register($autoload_function = UNKNOWN, bool $throw = true, bool $prepend = false): bool {}
 
 function spl_autoload_unregister($autoload_function): bool {}
 

ext/spl/php_spl_arginfo.h

@@ -29,7 +29,7 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_MASK_EX(arginfo_spl_autoload_functions, 0, 0, MA
 ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_spl_autoload_register, 0, 0, _IS_BOOL, 0)
-	ZEND_ARG_INFO_WITH_DEFAULT_VALUE(0, autoload_function, "null")
+	ZEND_ARG_INFO(0, autoload_function)
 	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, throw, _IS_BOOL, 0, "true")
 	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, prepend, _IS_BOOL, 0, "false")
 ZEND_END_ARG_INFO()