ci: drop python/3.9

Description

Drop support for python/3.9

Type of Change

• Remove python/3.9 CI tests
• Change python_requires to >=3.10

Additional Comments

Since CI pipelines of other projects will be triggered, this MR doesn't include any python/3.9 -> python/3.10 code changes. They could be pushed only after all projects drop python/3.9 CI pipelines, i.e. all these MR are accepted:

• bec!475 (merged)
• ophyd_devices!86 (merged)

Definition of Done

• Documentation is up-to-date.