chore: transition to shorter license headers (#6)

Transition from the GPL jumpscare to a more concise header:

	/*
     * Vencord, a Discord client mod
	 * Copyright (c) 2023 Vendicated and contributors
     *
	 * SPDX-License-Identifier: GPL-3.0
     */

Old files still keep the old headers, while eslint will now autofix the new header

Reviewed-on: https://codeberg.org/Ven/cord/pulls/6
Co-authored-by: Rini <rini@rinici.de>
Co-committed-by: Rini <rini@rinici.de>

src/plugins/shikiCodeblocks/previewExample.tsx

@@ -1,4 +1,4 @@
-/* eslint-disable header/header */
+/* eslint-disable simple-header/header */
 import React from "react";
 
 const handleClick = async () =>