refactor: simplify user picture test

[zetsux]

Description

This pull request makes minor adjustments to the TestUserService_ChangePicture test in picture_test.go, mostly simplifying the test setup by removing unnecessary user creation logic.

Test setup simplification:

• Removed the import of the custom error package errs, which is no longer needed due to the removal of user creation and error handling logic.
• Refactored the test to use a single expectedUser object directly, eliminating the previous steps of simulating user creation and error handling for GetUserByPrimaryKey and CreateNewUser. The test now focuses only on changing the user's picture.

Change

Check all options that are relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have performed a self-review of my code
• I have made sure that my fix is effective / my feature works
• All other features still works locally with my changes
• I have made API documentation and example response in Postman

[Copilot]

Pull Request Overview

This PR simplifies the TestUserService_ChangePicture test by removing unnecessary user creation setup and focusing solely on the picture change functionality. The refactoring eliminates redundant mock calls and intermediate variables while maintaining test coverage.

Key Changes:

• Removed unused errs package import
• Eliminated user creation logic and related mock setup
• Replaced multi-step user creation with direct expectedUser instantiation

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