(1.8) clang-format: fix the post-merge commit range
Pick some tricks from holo - we need stricter CI check. More importantly, once in post-merge we have other variables.
Namely: CI_COMMIT_BRANCH and CI_COMMIT_BEFORE_SHA
Signed-off-by: Emil Velikov emil.l.velikov@gmail.com (cherry picked from commit e006a34f)