Update expected middleware test error (#40918)

Fixes:
https://github.com/vercel/next.js/actions/runs/3128790934/jobs/5078100658#step:8:2223

test/e2e/middleware-general/test/index.test.ts

@@ -440,7 +440,7 @@ describe('Middleware Runtime', () => {
       const payload = readMiddlewareJSON(response)
       expect('error' in payload).toBe(true)
       expect(payload.error.name).toBe('AbortError')
-      expect(payload.error.message).toBe('The operation was aborted.')
+      expect(payload.error.message).toContain('The operation was aborted')
     })
 
     it(`should validate & parse request url from any route`, async () => {