Add support for Next.js 16

[dwayz94]

The package currently doesn't support Next.js 16, which was released recently. When trying to install next-auth-steam in a Next.js 16 project, npm fails with a dependency resolution error.

[Nekonyx]

Hello. Next.js 16 and next-auth@5 are technically supported. I'll publish a package.json fix within a couple of days.

[JamesIde]

Bump - has this been done?