GitAuto: Add unit tests to services/github/branch_manager.py

[gitauto-for-dev]

Resolves #440

What is the feature

Add unit tests to services/github/branch_manager.py to ensure its functionality and reliability. Additionally, create a constants.py file in the tests directory to define and manage constants for current and future test cases, promoting reuse and maintainability.

How to implement the feature and why

1. Create constants.py in the tests directory:

   • Define constants that will be used across multiple test modules. This centralizes common values, making tests easier to maintain and reducing duplication.

2. Add unit tests to services/github/branch_manager.py:

   • Develop comprehensive tests covering various functionalities of the branch_manager.py service.
   • Utilize constants from constants.py to maintain consistency and facilitate future test expansions.

This approach follows modern best practices by promoting code reuse, readability, and maintainability, ensuring that unit tests are robust and scalable.

Anything the issuer needs to do

No action required.

Test these changes locally

git fetch origin
git checkout gitauto-wes/issue-440-20241223-145216
git pull origin gitauto-wes/issue-440-20241223-145216