[PHP] - Removes trailing comma from ::flattenArray() (#20988)

* [PHP] - Removes trailing comma from ::flattenArray()

* Removes "mixed" type

* Missed one mixed

Author: jtreminio

modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache

@@ -324,7 +324,7 @@ class ObjectSerializer
      *
      * @return array [key => value] of formdata
      */
-    public static function toFormValue(string $key, mixed $value)
+    public static function toFormValue(string $key, $value)
     {
         if ($value instanceof \SplFileObject) {
             return [$key => $value->getRealPath()];
@@ -628,9 +628,9 @@ class ObjectSerializer
      * credit: https://github.com/FranBar1966/FlatPHP
      */
     private static function flattenArray(
-        mixed $source,
+        $source,
         array &$destination,
-        string $start = '',
+        string $start = ''
     ) {
         $opt = [
             'prefix'          => '[',

samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php

@@ -333,7 +333,7 @@ public static function toHeaderValue($value)
      *
      * @return array [key => value] of formdata
      */
-    public static function toFormValue(string $key, mixed $value)
+    public static function toFormValue(string $key, $value)
     {
         if ($value instanceof \SplFileObject) {
             return [$key => $value->getRealPath()];
@@ -637,9 +637,9 @@ public static function buildQuery(array $params, $encoding = PHP_QUERY_RFC3986):
      * credit: https://github.com/FranBar1966/FlatPHP
      */
     private static function flattenArray(
-        mixed $source,
+        $source,
         array &$destination,
-        string $start = '',
+        string $start = ''
     ) {
         $opt = [
             'prefix'          => '[',

samples/client/petstore/php/psr-18/lib/ObjectSerializer.php

@@ -333,7 +333,7 @@ public static function toHeaderValue($value)
      *
      * @return array [key => value] of formdata
      */
-    public static function toFormValue(string $key, mixed $value)
+    public static function toFormValue(string $key, $value)
     {
         if ($value instanceof \SplFileObject) {
             return [$key => $value->getRealPath()];
@@ -637,9 +637,9 @@ public static function buildQuery(array $params, $encoding = PHP_QUERY_RFC3986):
      * credit: https://github.com/FranBar1966/FlatPHP
      */
     private static function flattenArray(
-        mixed $source,
+        $source,
         array &$destination,
-        string $start = '',
+        string $start = ''
     ) {
         $opt = [
             'prefix'          => '[',