remove circular ExportError import from SSG worker (vercel#68858)

These are technically different kinds of errors and results in the
worker importing everything in `build`, which was an unintentional side
effect of vercel#68546.

packages/next/src/export/worker.ts

@@ -43,7 +43,6 @@ import {
 } from '../build/turborepo-access-trace'
 import type { Params } from '../client/components/params'
 import { needsExperimentalReact } from '../lib/needs-experimental-react'
-import { ExportError } from '.'
 
 const envConfig = require('../shared/lib/runtime-config.external')
 
@@ -55,6 +54,10 @@ class TimeoutError extends Error {
   code = 'NEXT_EXPORT_TIMEOUT_ERROR'
 }
 
+class ExportPageError extends Error {
+  code = 'NEXT_EXPORT_PAGE_ERROR'
+}
+
 async function exportPageImpl(
   input: ExportPageInput,
   fileWriter: FileWriter
@@ -396,15 +399,15 @@ export async function exportPages(
         // If there was an error in the export, throw it immediately. In the catch block, we might retry the export,
         // or immediately fail the build, depending on user configuration. We might also continue on and attempt other pages.
         if (result && 'error' in result) {
-          throw new ExportError()
+          throw new ExportPageError()
         }
 
         // If the export succeeds, break out of the retry loop
         break
       } catch (err) {
         // The only error that should be caught here is an ExportError, as `exportPage` doesn't throw and instead returns an object with an `error` property.
         // This is an overly cautious check to ensure that we don't accidentally catch an unexpected error.
-        if (!(err instanceof ExportError || err instanceof TimeoutError)) {
+        if (!(err instanceof ExportPageError || err instanceof TimeoutError)) {
           throw err
         }
 
@@ -424,7 +427,7 @@ export async function exportPages(
           }
           // If prerenderEarlyExit is enabled, we'll exit the build immediately.
           if (nextConfig.experimental.prerenderEarlyExit) {
-            throw new ExportError(
+            throw new ExportPageError(
               `Export encountered an error on ${pageKey}, exiting the build.`
             )
           } else {