Bump pbr from 5.5.1 to 5.6.0 in /requirements (#17025)
Bump pbr from 5.5.1 to 5.6.0 in /requirements (#17025)

Bumps [pbr](https://docs.openstack.org/pbr/latest/) from 5.5.1 to 5.6.0.

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
mozilla/olympia,mozilla/olympia,mozilla/addons-server,wagnerand/addons-server,mozilla/olympia,bqbn/addons-server,wagnerand/addons-server,mozilla/addons-server,mozilla/addons-server,diox/olympia,diox/olympia,bqbn/addons-server,mozilla/addons-server,diox/olympia,mozilla/olympia,wagnerand/addons-server,bqbn/addons-server,diox/olympia,wagnerand/addons-server,bqbn/addons-server