Fix @vercel/og license SPDX expression (#74745)

### What?

A minor fix to the `package.json` for `@vercel/og`; there is a typo on
the SPDX license ID for MPL-2.0 which is causing the license ID to not
be correctly extracted by some automated tooling (one example is
https://github.com/CycloneDX/cyclonedx-webpack-plugin, meaning that the
license ID isn't correctly identified).

### Why?

For apps that use automated tooling to generate an exhaustive list of
dependencies, it's useful to have the license identified automatically
and for this to be a valid SPDX identifier to be able to group
dependencies together.

Co-authored-by: Jiachi Liu <[email protected]>

Author: matmannion

packages/next/src/compiled/@vercel/og/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@vercel/og",
   "version": "0.6.4",
-  "LICENSE": "MLP-2.0",
+  "license": "MPL-2.0",
   "type": "module",
   "main": "./index.node.js",
   "exports": {

packages/next/taskfile.js

@@ -222,7 +222,7 @@ export async function copy_vercel_og(task, opts) {
     {
       name: '@vercel/og',
       version: require('@vercel/og/package.json').version,
-      LICENSE: 'MLP-2.0',
+      license: 'MPL-2.0',
       type: 'module',
       main: './index.node.js',
       exports: {