Downgrade python dependency floor to `python = "^3.9"`

Downgrade python dependency floor to python = "^3.9"

Background

When poetry was introduced to the identity-lib repo the python floor was set at python = "^3.10"

We may not want to bother with this ticket if we action https://gitlab.developers.cam.ac.uk/uis/devops/iam/identity-photos-service/photo-api/-/issues/109

Acceptance Criteria

• Updated identity-lib is available from PyPI