Make sure to add trailing slash on paths

[DominicOram]

Fixes DiamondLightSource/mx-bluesky#454

Instructions to reviewer on how to test:

1. Confirm tests still 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 94.89%. Comparing base (350ca72) to head (93f8f07).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #779   +/-   ##
=======================================
  Coverage   94.89%   94.89%           
=======================================
  Files         115      115           
  Lines        4640     4640           
=======================================
  Hits         4403     4403           
  Misses        237      237           

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[olliesilvester]

Green ticks!