Httpx Response content is not set/read, causing JSON parsing errors

[Yun-Kim]

Hi there, running into the same issue as #832. It seems like getting rid of the manual step to set response._content, as well as mocking the httpx.Response.read() function resulted in the following error by httpx (occurs non-deterministically in my CI):

httpx.ResponseNotRead: Attempted to access streaming response content, without having called `read()` 

I haven't narrowed down the non-deterministic nature of this bug, but it seems like there's two solutions to this:

1. Re-insert the manual step to set response._content that was removed by Make httpx_stubs generate cassettes consistent with other stubs. #649
2. Don't patch httpx.Response.read (not sure what the implications of this is)

This is causing a good amount of flakiness in my CI, so would really appreciate any insights/help getting this fixed. Thanks!