Fix various compatibility issues with PHP 8

libs/swiftmailer/classes/Swift/Mime/ParameterizedHeader.php

@@ -0,0 +1,34 @@
+<?php
+
+/*
+ * This file is part of SwiftMailer.
+ * (c) 2004-2009 Chris Corbyn
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+/**
+ * A MIME Header with parameters.
+ *
+ * @author Chris Corbyn
+ */
+interface Swift_Mime_ParameterizedHeader extends Swift_Mime_Header
+{
+    /**
+     * Set the value of $parameter.
+     *
+     * @param string $parameter
+     * @param string $value
+     */
+    public function setParameter($parameter, $value);
+
+    /**
+     * Get the value of $parameter.
+     *
+     * @param string $parameter
+     *
+     * @return string
+     */
+    public function getParameter($parameter);
+}