Fix jungfrau driver prefix on i24

[ndevenish]

The commissioning jungfrau IOC serves its FastCS PVs at the root prefix, so the CAM: suffix pointed at BL24I-EA-JFRAU-01:CAM:PVI, which does not exist. The device failed to connect at startup and blueapi dropped it, so plans injecting it were rejected with 'Device jungfrau cannot be found'.

Instructions to reviewer on how to test:

1. Do thing x
2. Confirm thing y happens

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 99.20%. Comparing base (3b77d81) to head (a69e86e).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2187      +/-   ##
==========================================
+ Coverage   99.16%   99.20%   +0.04%     
==========================================
  Files         354      367      +13     
  Lines       13842    14589     +747     
==========================================
+ Hits        13726    14473     +747     
  Misses        116      116              

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