build pipelines get hash is unstable.

[purelind]

Currently we get release branch commit sha1 through a python script, this step is not stable.

We need to refactor this part of the logic, directly calling the GitHub API for implementation, and adding error retry to ensure stability.

https://github.com/PingCAP-QE/ci/blob/main/jenkins/pipelines/cd/pre-release-community-docker.groovy#L119-L127