Allow overriding the scheme used in websocket_connect to support wss

[shevron]

This is my fix for #47. It allows passing scheme= to a websocket connection. I also took the liberty of passing any arguments to websocket_connect down to the WebSocketSession constructor, similar to how all the other get, post etc. method just pass arguments to open.

Happy to fix if there is any feedback.

[codecov-commenter]

Codecov Report

Merging #48 (9821cb8) into master (0e92f98) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
+ Coverage   87.53%   87.56%   +0.03%     
==========================================
  Files           6        6              
  Lines         409      410       +1     
==========================================
+ Hits          358      359       +1     
  Misses         51       51              

Impacted Files	Coverage Δ
async_asgi_testclient/testing.py	89.04% <100.00%> (ø)
async_asgi_testclient/websocket.py	74.41% <100.00%> (+0.30%)	⬆️

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[shevron]

Note that the formatting changes are caused by running the latest black (couldn't get the version specified in test-requirements.txt to run with Python 3.9.9). I ran it because otherwise Travis wouldn't pass.

[masipcat]

Thank you for your contribution! Right now I'm on holidays so I'll do the release when I come back (in a couple of weeks)