[BUILD] Use right branch when checking against Hive

Right now we always run hive tests in branch-1.4 PRs because we compare whether the diff against master involves hive changes. Really we should be comparing against the target branch itself.

Author: Andrew Or <andrew@databricks.com>

Closes #6629 from andrewor14/build-check-hive and squashes the following commits:

450fbbd [Andrew Or] [BUILD] Use right branch when checking against Hive