fix: Deduplication of failures caused by malformed JSON payload

[Stranger6667]

Fixes #1518

[codecov-commenter]

Codecov Report

Merging #1519 (8822ef0) into master (b0d97a0) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1519   +/-   ##
=======================================
  Coverage   99.15%   99.15%           
=======================================
  Files          91       91           
  Lines        7012     7014    +2     
  Branches     1237     1237           
=======================================
+ Hits         6953     6955    +2     
  Misses         35       35           
  Partials       24       24           

Impacted Files	Coverage Δ
src/schemathesis/failures.py	100.00% <100.00%> (ø)

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