Resolve event loop closed issue when trying a second attempt with flaky

[wjsi]

When using flaky along with pytest-asyncio, for instance,

@flaky.flaky(3)
@pytest.mark.asyncio
async def test_errors():
    raise ValueError

when the first attempt failed, the second attempt will raise RuntimeError: Event loop is closed (given box/flaky#166). The reason is that the wrapper

pytest-asyncio/pytest_asyncio/plugin.py

Line 185 in 6ec7647

def wrap_in_sync(func, _loop):

will be called twice in pytest_pyfunc_call and the previous closed loop is still used. The resolution is to record the original function and wrap the original function every time.

Fixes #178

[wjsi]

@Tinche please take a look at this PR :)

[asvetlov]

LGTM
Another solution can be moving the wrapping from the async test calling stage to tests collection stage.
Might require more lines change though.

[codecov-commenter]

Codecov Report

Merging #220 (58c7bb5) into master (f21e0da) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
+ Coverage   95.86%   95.94%   +0.08%     
==========================================
  Files           2        2              
  Lines         145      148       +3     
==========================================
+ Hits          139      142       +3     
  Misses          6        6              

Impacted Files	Coverage Δ
pytest_asyncio/plugin.py	95.91% <100.00%> (+0.08%)	⬆️

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