Pin ophyd_async due to pydantic

[DominicOram]

See #679

Instructions to reviewer on how to test:

1. Re-install dodal and confirm dependencies are happy, particularly we're still on pydantic<2.0

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[d-perl]

I think (from running the tests) that dodal is not actually compatible with ophyd-async 0.3.1 (e.g. soft_signal_r_and_setter doesn't take units as used by i22 dcm in this version...), should probably remove the lower bound or at least increase it to the version which works

[d-perl]

lgtm, thanks