fix: preserve ARQ enqueue_job __kwdefaults__ after patching

[danmr]

Problem:

• The ARQ integration loses __kwdefaults__ when patching the enqueue_job method
• This causes issues when filtering kwargs in custom implementations

Solution:

• Save original __kwdefaults__ before patching
• Restore them in the patched function

---

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[sentrivana]

Thanks @danmr.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.84%. Comparing base (fd22494) to head (380df84).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3903      +/-   ##
==========================================
- Coverage   79.89%   79.84%   -0.05%     
==========================================
  Files         139      139              
  Lines       15417    15419       +2     
  Branches     2623     2623              
==========================================
- Hits        12317    12311       -6     
- Misses       2227     2236       +9     
+ Partials      873      872       -1     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/arq.py	87.02% <100.00%> (+0.20%)	⬆️

... and 3 files with indirect coverage changes