Update stalled ensure log to use debug instead (#39826)

This updates the stalled ensure log to use debug instead the log isn't really actionable by the user and is more so meant for debugging purposes.
x-ref: slack thread

packages/next/server/dev/on-demand-entry-handler.ts

@@ -1,5 +1,5 @@
 import type ws from 'ws'
-import * as Log from '../../build/output/log'
+import origDebug from 'next/dist/compiled/debug'
 import type { webpack } from 'next/dist/compiled/webpack/webpack'
 import type { NextConfigComplete } from '../config-shared'
 import { EventEmitter } from 'events'
@@ -23,6 +23,8 @@ import {
   COMPILER_NAMES,
 } from '../../shared/lib/constants'
 
+const debug = origDebug('next:on-demand-entry-handler')
+
 /**
  * Returns object keys with type inferred from the object key
  */
@@ -517,7 +519,7 @@ export function onDemandEntryHandler({
     async ensurePage(page: string, clientOnly: boolean): Promise<void> {
       const stalledTime = 60
       const stalledEnsureTimeout = setTimeout(() => {
-        Log.warn(
+        debug(
           `Ensuring ${page} has taken longer than ${stalledTime}s, if this continues to stall this may be a bug`
         )
       }, stalledTime * 1000)