test: update e2e/app-dir/metadata/metadata.test.ts

Author: devjiwonchoi

test/e2e/app-dir/metadata/metadata.test.ts

@@ -710,10 +710,7 @@ describe('app dir - metadata', () => {
 
     it('should support root dir robots.txt', async () => {
       const res = await next.fetch('/robots.txt')
-      expect(res.headers.get('content-type')).toBe(
-        // In dev, sendStatic() is used to send static files, which adds MIME type.
-        isNextDev ? 'text/plain; charset=UTF-8' : 'text/plain'
-      )
+      expect(res.headers.get('content-type')).toBe('text/plain; charset=UTF-8')
       expect(await res.text()).toContain('User-Agent: *\nDisallow:')
       const invalidRobotsResponse = await next.fetch('/title/robots.txt')
       expect(invalidRobotsResponse.status).toBe(404)