Add await to response.json() for async ApiResponse class

[Ekwinder]

The current async APIResponse class documentation in API Reference has an incorrect line in the example -

assert response.json()["name"] == "foobar"

As the async APIResponse response.json() returns a coroutine, this line will raise a TypeError: 'coroutine' object is not subscriptable exception.

Replacing it with

json_data = await response.json()
assert json_data["name"] == "foobar"

will solve this and show the correct way to use response.json()

[Ekwinder]

@microsoft-github-policy-service agree

[Skn0tt]

The change looks good, but it's in the wrong place. This repository contains build outputs for the docs. Please open this PR against https://github.com/microsoft/playwright/blob/fffd87af1d65bc4d91ecf2eb47878f59b2ede514/docs/src/api/class-apiresponse.md#L16

[Ekwinder]

Thanks @Skn0tt will raise a PR in the correct repo.