Update @sentry/nextjs package.json to support Next.js 12

[The issue](https://github.com/getsentry/sentry-javascript/pull/4027) holding up Sentry's support of Next.js 12 has been merged, however it still can't use it on Next 12 because @sentry/nextjs's [package.json](https://github.com/getsentry/sentry-javascript/blob/master/packages/nextjs/package.json#L37) specifies a dependency on Next v11.

Can we update @sentry/nextjs `package.json`?