When you make a change to the LESS in /theme/bootstrapbase/less... then CiBoT checks to see that you have either altered thirdpartylibs.xml or readme_moodle.txt however its looking for readme_moodle.txt in /theme/bootstrapbase/less/bootstrap/ when in fact the file is in /theme/bootstrapbase/ (https://github.com/moodle/moodle/blob/master/theme/bootstrapbase/readme_moodle.txt) and thus even if you have changed this file as you should CiBoT thinks that you have not!

So....

modification to third party library (theme/bootstrapbase/less/bootstrap) without update to theme/bootstrapbase/thirdpartylibs.xml or theme/bootstrapbase/less/bootstrap/readme_moodle.txt

should be:

modification to third party library (theme/bootstrapbase/less/bootstrap) without update to theme/bootstrapbase/thirdpartylibs.xml or theme/bootstrapbase/readme_moodle.txt