Update dependencies, and use new Poetry installer in CI

Poetry 1.2.0 which was announced recently comes with e.g. new installer (and btw plugin support). The old one will be deprecated Jan 1, 2023, see the failure of the pipeline in the master: https://gitlab.cern.ch/lhcb-core/nightly-builds/lb-nightly-rpc/-/jobs/24538054.

This MR changes the way CI installs the Poetry.