Make sure that the aperture scatterguard position is set correctly

[DominicOram]

See DiamondLightSource/mx-bluesky#463

Instructions to reviewer on how to test:

1. Confirm tests pass

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 94.91%. Comparing base (44abdd2) to head (1f8c646).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #784      +/-   ##
==========================================
- Coverage   94.91%   94.91%   -0.01%     
==========================================
  Files         115      115              
  Lines        4665     4664       -1     
==========================================
- Hits         4428     4427       -1     
  Misses        237      237              

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[rtuck99]

Approved