fix: correct typo in issue_activities_task.py file variable names

[ShaikhNaasir]

• Fix dropped_assginees → dropped_assignees
• Fix added_asignee → added_assignee
• Ensure consistent naming convention throughout function

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[!NOTE] Corrects variable name typos in track_assignees to use added_assignee and dropped_assignees consistently.

• Updates loops and UUID checks to reference the corrected variables
• Ensures proper User lookups and IssueSubscriber creation/removal activities

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Summary by CodeRabbit

• Bug Fixes
  • Corrected assignee-handling in issue activity tracking so changes to assignees are logged and resolved accurately, improving reliability of assignee updates and history.

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