fix dependencies resolution in CI pipeline
After PyYAML >=6 (used also in lb-nightly-configuration) dropped support for Python 2.
Needed to fix the pipeline in !901 (merged) (https://gitlab.cern.ch/lhcb-core/LHCbNightlyConf/-/jobs/24664352)
After PyYAML >=6 (used also in lb-nightly-configuration) dropped support for Python 2.
Needed to fix the pipeline in !901 (merged) (https://gitlab.cern.ch/lhcb-core/LHCbNightlyConf/-/jobs/24664352)