Add required project for Neutron / OSP 17.1

There was a feature backported downstream that requires
a newer version of Neutron-Lib project installed locally.
Thanks to tox-siblings role, we can install the version
of code for liniting specified as dependent repository.

znoyder/config.d/42-override-OSP-17.yml

@@ -313,6 +313,8 @@ override:
         vars:
           extra_commands:
             - dnf install -y python3-hacking python3-neutron-lib-tests
+          required-projects:
+            - python-neutron-lib
 
   'nova':
     'osp-17.0':