Fix metadata bugs in ERA5, Narclim

[marc-white]

Fixes #286.

This PR contains metadata format fixes for the experiments era5-rt52 and narclim2-zz63.

@charles-turner-1 before approving the PR and merging, you'll need to copy both of the new files over to the live location on xp65 (I found a stray comma in the narclim keywords list that I dealt with).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.44%. Comparing base (9d540e2) to head (67db84e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #287   +/-   ##
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  Coverage   98.44%   98.44%           
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  Files          11       11           
  Lines         838      838           
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  Hits          825      825           
  Misses         13       13           

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[charles-turner-1]

I've pushed a commit including an update to the short description on NARCliM too - mirroring the xp65 version.