Using older version of Gunicorn

Description

Currently, using version 22 of Gunicorn in pyproject.toml gunicorn = "^22.0.0". Other repos are requiring version 23, so there is a versioning conflict.

Further details

As this is a library this constraint should be widened.

Task list

Acceptance criteria

• The package uses more permissive constraints, allowing it to be used in client systems on gunicorn 22 and 23.
• Current functionality is maintained

Links/references

https://gitlab.developers.cam.ac.uk/uis/devops/iam/card-database/card-api