license: Exclude new gitlab tmp folder from license check

GitLab-Runners greater or equal to 16.6 now materialises
all file-types (e.g. CI/CD variables) in a directory that lives
next to $CI_PROJECT_DIR and ends in .tmp instead of using
/tmp as it did before. Hence, exclude all files in the new
`.tmp` folder from license check.

Signed-off-by: Angelina Dobardzieva <angelina.dobardzieva@arm.com>