packages defined in .req or in .packages file not being installed in el9stream mock env

Pushing https://github.com/oVirt/python-ovirt-engine-sdk4/pull/8 fails on 

[2021-08-24T14:33:13.200Z] error: Failed build dependencies:[2021-08-24T14:33:13.200Z] error: Failed build dependencies:
[2021-08-24T14:33:13.200Z] libxml2-devel is needed by python-ovirt-engine-sdk4-4.4.16-0.1.master.20210824143256.el9.x86_64
[2021-08-24T14:33:13.200Z] python3-devel is needed by python-ovirt-engine-sdk4-4.4.16-0.1.master.20210824143256.el9.x86_64

despite the requirements are correctly listed in the configuration for the job.

See https://jenkins.ovirt.org/blue/organizations/jenkins/oVirt_python-ovirt-engine-sdk4_standard-check-pr/detail/oVirt_python-ovirt-engine-sdk4_standard-check-pr/44/pipeline