fix(worker): Handle missing JaCoCo branch attributes in upload processor

[sentry]

This PR addresses a KeyError: 'cb' occurring in app.tasks.upload.UploadProcessor when processing JaCoCo XML reports.

The root cause was identified in apps/worker/services/report/languages/jacoco.py, where the parser directly accessed attr["cb"] and attr["mb"] for <line> XML elements. JaCoCo legitimately omits these attributes when a line has no branch coverage data, causing a KeyError when such reports were encountered.

The fix replaces direct dictionary access (e.g., attr["cb"]) with safe .get() calls (e.g., attr.get("cb", "0")). This ensures that if cb or mb attributes are missing, they default to "0", preventing the KeyError and correctly interpreting lines without explicit branch coverage as having zero branch coverage.

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Fixes WORKER-X6N

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.83%. Comparing base (d8942db) to head (3df4687).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1879   +/-   ##
=======================================
  Coverage   91.83%   91.83%           
=======================================
  Files        1332     1332           
  Lines       51830    51830           
  Branches     1647     1647           
=======================================
  Hits        47598    47598           
  Misses       3911     3911           
  Partials      321      321           

Flag	Coverage Δ
workerintegration	58.51% <0.00%> (ø)
workerunit	90.39% <100.00%> (ø)

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[codecov-notifications]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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