Keyfix eccodes 2v38

[pp-mo]

This also fixes a numpy2 problem.

Once working, should unblock the lockfile update (see #550).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.60%. Comparing base (180c24e) to head (1719b7e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #578   +/-   ##
=======================================
  Coverage   89.60%   89.60%           
=======================================
  Files           8        8           
  Lines        2473     2473           
  Branches      420      420           
=======================================
  Hits         2216     2216           
  Misses        159      159           
  Partials       98       98           

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[pp-mo]

Whoops I should have made this a Draft.

Unpinning numpy 2 reveals that the "other" problem isn't really fixed
as it breaks at least the unit-test in src/iris_grib/tests/unit/load_convert/test__hindcast_fix.py::TestHindcastFix

I am working on this, will sort it out + unblock the lockfile upate.
I'm thinking it may then be good to issue a "bugfix release" -- or similar, given that we don't have a major release yet (!!)