Treat Playwright tests with parallism as separate (for timeouts)

If you've got a few related but long-running tests in a single file right now, you risk running into timeouts (120 or 240s?). Checkly currently considers each Browser Check to have one single global timeout.

That means that creating a file like this:

```
import { test } from './fixtures' test.use({ baseURL: '/' }) test.describe.configure({ mode: 'parallel' })

test.beforeEach(async ({ page }) => {
...
})

test('xxx', async ({ page }) => {
...
})

test('xxx', async ({ page }) => {
...
})

test('xxx', async ({ page }) => {
...
})
```

You're very likely to hit a timeout if any of the tests are long-running, even though it seems like they would all run in parallel and therefor not hit a timeout.

The solution right now is to make multiple `.spec.ts` files. This does resolve the timeout problem, but you loose out on having easily shared code with features like `test.beforeEach()`.