feat: pkg/util/github/branch enhancement

[jxs1211]

Signed-off-by: xian-jie.shen 327411586@qq.com

Pre-Checklist

Note: please complete ALL items in the following checklist.

• I have read through the CONTRIBUTING.md documentation.
• My code has the necessary comments and documentation (if needed).
• I have added relevant tests

Description

add ut for pkg/util/github/branch

Related Issues

see #833 for the details

New Behavior (screenshots if needed)

[going@dev github]$ go tool cover -func=coverage.out
github.com/devstream-io/devstream/pkg/util/github/branch.go:11:                 NewBranch                               100.0%
github.com/devstream-io/devstream/pkg/util/github/branch.go:38:                 DeleteBranch                            100.0%
github.com/devstream-io/devstream/pkg/util/github/commit.go:11:                 GetLastCommit                           0.0%

[daniel-hutao]

Thank you for your contribution! UT work is important. I'll approve this pr in no time, but I still have a tip for you: try to use the ginkgo framework to write UT, it will be much easier.