Duplicated triggering of Koji builds for comment commands

[lbarcziova]

Example: https://src.fedoraproject.org/rpms/packit/pull-request/1301#comment-223227

This comment triggered the koji_build job twice (hence the followup 2 comments). With @nforro we suspect that this is caused by trigger: commit | koji_build in our koji_build job configuration (here).