Fix missing cause

`TURBOPACK=1 TURBOPACK_DEV=1 pnpm test test/integration/edge-runtime-streaming-error/test/index.test.ts` will now produce an error
that does have a `originalCodeFrame` and therefore
goes through the codepath previously omitting cause.

`logErrorWithOriginalStack` will be gone soon anyway.

packages/next/src/server/lib/router-utils/setup-dev-bundler.ts

@@ -1046,10 +1046,8 @@ async function startWatcher(opts: SetupOpts) {
                 frames
               )
 
-              const error: NextError = new Error(err.message)
-              error.stack = stack
-              error.digest = err.digest
-              errorToLog = error
+              err.stack = stack
+              errorToLog = err
             } else {
               errorToLog = err
             }