Update polardb_build.sh

[digoal]

fix error:

fatal: ambiguous argument 'HEAD~1': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

[polardb-bot[bot]]

Hi @digoal ~ Thanks for your contribution in this PR. ❤️

Please make sure that your PR conforms the standard, and has passed all the checks.

We will review your PR as soon as possible.

[polardb-bot[bot]]

Hey @digoal :

Congratulations~ 🎉 Your commit has passed all the checks. Please wait for further manual review.

[mrdrivingduck]

@digoal Pull request should be raised to branch POLARDB_11_DEV.

[mrdrivingduck]

/close