test: update error code

Author: devjiwonchoi

test/development/error-overlay/index.test.tsx

@@ -14,7 +14,7 @@ describe('DevErrorOverlay', () => {
 
     const errorCode = await browser.elementByCss('[data-nextjs-error-code]')
     const code = await errorCode.getAttribute('data-nextjs-error-code')
-    expect(code).toBe('E846')
+    expect(code).toBe('E838')
   })
 
   it('sends feedback when clicking helpful button', async () => {