the double dot gets only commits not in the left side of the double dot.
The right side assumes HEAD.
This will allow us to fetch the correct list of new or modified files in the current branch.
This makes it possible to run the script locally even if `TRAVIS_PULL_REQUEST` is not set.
Currently, it results in an error:
tools/scripts/ci_build.sh: line 2: [: !=: unary operator expected
This script is intended to identify common test file formatting errors
prior to their acceptance into the project. It is designed to support
future extensions for additional validation rules.
