Code Quality: Preserve string[] input type in wp_parse_list() return.

This prevents unintentional widening of a `string[]` input to a `scalar[]` output, since strings are scalars.

Follow-up to r62797.

See #64898.


git-svn-id: https://develop.svn.wordpress.org/trunk@62835 602fd350-edb4-49c9-b593-d223f7449a82

Author: westonruter

src/wp-includes/functions.php

@@ -5034,9 +5034,13 @@ function wp_parse_args( $args, $defaults = array() ) {
  * @since 5.1.0
  *
  * @param mixed[]|string $input_list List of values.
- * @return array Array of values. A string is split into a list, while an array
+ * @return array Array of scalar values. A string is split into a list, while an array
  *               keeps its keys, so the result is not necessarily a list.
- * @phpstan-return ( $input_list is string ? list<string> : array<scalar> )
+ * @phpstan-return (
+ *     $input_list is string ? list<string> : (
+ *         $input_list is array<string> ? array<string> : array<scalar>
+ *     )
+ * )
  */
 function wp_parse_list( $input_list ): array {
 	if ( ! is_array( $input_list ) ) {