Merge pull request #266 from level-level/revert_pr_263

Revert #263, fixes jsonSerialize fatal error on php 7.4 or lower

Author: NielsdeBlaauw

src/WordPress_Object/Clarkson_Object.php

@@ -627,7 +627,7 @@ public function get_comments( array $args = array() ): array {
 	 * We can't just return $this->_post, because these values will only return raw unfiltered data.
 	 */
 	#[\ReturnTypeWillChange]
-	public function jsonSerialize(): mixed {
+	public function jsonSerialize() {
 		$data              = array();
 		$data['id']        = $this->get_id();
 		$data['link']      = $this->get_permalink();