Exclude PreqJobNotFinishedError from Sentry reporting (#8614)

This error is a normal, transient condition raised when a dependent job
runs before its prerequisite jobs have completed. Sidekiq's default retry
handles it correctly — the only issue was Sentry noise.

Closes #8597

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: iHiD

config/initializers/sentry.rb

@@ -14,7 +14,7 @@
     config.environment = Rails.env
     config.breadcrumbs_logger = %i[active_support_logger http_logger]
     config.send_default_pii = false
-    config.excluded_exceptions += ['ActiveRecord::Deadlocked']
+    config.excluded_exceptions += ['ActiveRecord::Deadlocked', 'MandateJob::PreqJobNotFinishedError']
     config.before_send = SENTRY_ACTIVE_STORAGE_FILTER
   end
 end