fix(worker): handle None branch in notification matching

[sentry]

This PR addresses a TypeError occurring in the app.tasks.notify.Notify task. The error, "TypeError: expected string or bytes-like object, got 'NoneType'", was traced back to re.match() being called with None as its string argument.

The root cause was identified in apps/worker/services/notification/notifiers/status/base.py, where can_we_set_this_status passes head.branch directly to the match() helper function in helpers/match.py. For certain commits (predominantly from the milvus-io/milvus repository), head.branch can be None.

To fix this, apps/worker/helpers/match.py has been updated. The match() function now explicitly handles None values for its string parameter by coercing them to an empty string (""). This prevents the TypeError and ensures that commits without an associated branch correctly fail to match any branch-specific notification filters.

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Fixes WORKER-R8F

[codecov-notifications]

Codecov Report

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

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.83%. Comparing base (d8942db) to head (334eb4a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1880   +/-   ##
=======================================
  Coverage   91.83%   91.83%           
=======================================
  Files        1332     1332           
  Lines       51830    51831    +1     
  Branches     1647     1647           
=======================================
+ Hits        47598    47599    +1     
  Misses       3911     3911           
  Partials      321      321           

Flag	Coverage Δ
workerintegration	58.51% <100.00%> (+<0.01%)	⬆️
workerunit	90.39% <100.00%> (+<0.01%)	⬆️

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