fix: Use-after-free in async $ref resolution when multiple refs target the same external URL with different fragments

[Stranger6667]

Fixes #906

[codecov]

Codecov Report

❌ Patch coverage is 97.93814% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.39%. Comparing base (f4bdaa0) to head (26cf72a).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/jsonschema-referencing/src/registry.rs	97.93%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #921      +/-   ##
==========================================
+ Coverage   94.38%   94.39%   +0.01%     
==========================================
  Files          78       78              
  Lines       17537    17611      +74     
==========================================
+ Hits        16552    16624      +72     
- Misses        985      987       +2     

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[codspeed-hq]

CodSpeed Performance Report

Merging #921 will not alter performance

_{Comparing dd/fix-panic-2 (26cf72a) with master (f4bdaa0)}

Summary

✅ 61 untouched