Fix typo in asgi client

[ahopkins]

This was a typo.

[codecov]

Codecov Report

Merging #2014 (0165c9c) into master (afb527b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2014   +/-   ##
=======================================
  Coverage   91.45%   91.45%           
=======================================
  Files          28       28           
  Lines        3171     3171           
  Branches      571      571           
=======================================
  Hits         2900     2900           
  Misses        192      192           
  Partials       79       79           

Impacted Files	Coverage Δ
sanic/app.py	94.91% <ø> (ø)

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