fix: Add Git Username env variable #4315

[thiha-min-thant]

Proposed changes

• Added support for setting the Git username as an environment variable (GIT_USERNAME) to ensure compatibility with Bitbucket repositories.
• This change addresses an issue where Bitbucket requires the username explicitly, and the default system username did not work correctly for authentication.
• Fixed Unable to import a litmushub from bitbucket(private repository) #4315

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• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices applies)

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Dependency

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[amityt]

LGTM! Thanks for the fix @thiha-min-thant 🙌🏼