Fix broken link.

[pp-mo]

Problem has appeared here : https://github.com/SciTools/iris/actions/runs/12171348115/job/33948080471
So should unblock at least #6243
(but expect further problems from it)

It does look to me like the url target has definitely changed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.83%. Comparing base (67d0b07) to head (e15831d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6246   +/-   ##
=======================================
  Coverage   89.83%   89.83%           
=======================================
  Files          88       88           
  Lines       23315    23315           
  Branches     4338     4338           
=======================================
  Hits        20945    20945           
  Misses       1644     1644           
  Partials      726      726           

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