fix(nodejs-middleware): await for body cloning to be properly finalized (#85418)
Fixes https://github.com/vercel/next.js/issues/85416.
This is a follow up to https://github.com/vercel/next.js/pull/77662,
where the Node.js middleware was fixed to also support reading (and
duplicating) the body's request before being passed to the server
action.
However, in that PR, an `await` was missed while calling the
[.finalize()](https://github.com/vercel/next.js/blob/1b45163bce3dab30d7a79dff95238b84016b54c2/packages/next/src/server/body-streams.ts#L39)
method, which returns a Promise. That missing `await` would sometimes
cause a bug, where the server action would be invoked before the body
was completely cloned, causing the bug mentioned in the issue above.
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Co-authored-by: JJ Kasper <jj@jjsweb.site>