Adapt to minor breaking change in websocket API

[graebm]

Adapt to changes from awslabs/aws-c-http#409

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Base: 81.33% // Head: 81.18% // Decreases project coverage by -0.14% ⚠️

Coverage data is based on head (8699ccd) compared to base (c2bc310).
Patch coverage: 37.50% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #243      +/-   ##
==========================================
- Coverage   81.33%   81.18%   -0.15%     
==========================================
  Files          14       14              
  Lines        7183     7181       -2     
==========================================
- Hits         5842     5830      -12     
- Misses       1341     1351      +10     

Impacted Files	Coverage Δ
source/client.c	65.05% <0.00%> (-0.77%)	⬇️
source/v5/mqtt5_client.c	88.41% <75.00%> (-0.02%)	⬇️

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