[test] Improve app-basepath assertion error (#86725)
To make it print out what the second request is when this flake happens:
```
● app dir - basepath › should only make a single RSC call to the current page (/base/refresh?foo=bar)
expect(received).toBe(expected) // Object.is equality
Expected: 1
Received: 2
91 | await browser.elementByCss('button').click()
92 | await retry(async () => {
> 93 | expect(rscRequests.length).toBe(1)
| ^
94 | expect(rscRequests[0]).toContain(`${next.url}${path}`)
95 | })
96 | }
at toBe (e2e/app-dir/app-basepath/index.test.ts:93:36)
at fn (lib/next-test-utils.ts:797:20)
at e2e/app-dir/app-basepath/index.test.ts:92:7
```
