Wait for set to finish after focus mirrors finish slew

[DominicOram]

Part of DiamondLightSource/mx-bluesky#277

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}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.00%. Comparing base (eece064) to head (ef88f63).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #800   +/-   ##
=======================================
  Coverage   94.99%   95.00%           
=======================================
  Files         115      115           
  Lines        4719     4720    +1     
=======================================
+ Hits         4483     4484    +1     
  Misses        236      236           

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[rtuck99]

Approved