as recommended in several places, use `origin/master`

1 job for !960 with clang-format-gitlab-ci in 1 minute and 6 seconds (queued for 7 seconds)
detached
Status Name Job ID Coverage
  Build
failed clang_format #118469

00:01:06

 
Name Stage Failure
failed
clang_format Build
Saving to: '.clang-format'

0K .. 100% 59.4M=0s

2021-07-17 05:34:40 (59.4 MB/s) - '.clang-format' saved [2547/2547]

$ git diff-tree --no-commit-id --name-only -r origin/$CI_MERGE_REQUEST_TARGET_BRANCH_NAME -r $CI_COMMIT_SHA -- | grep -P '[.](c|cc|cpp|hpp|h)$' | xargs --no-run-if-empty --verbose clang-format-11 --dry-run -Werror
Cleaning up file based variables
ERROR: Job failed: exit code 1