Pin iris version to avoid issue with dask

Fixes the following error when solving Iris cubes:
> self.delayed_completion().compute()
E AttributeError: 'tuple' object has no attribute 'compute'

Author: valentinaschueller

conda_environment.yml

@@ -3,7 +3,6 @@ channels:
 dependencies:
     - python>=3.8
     - pip
-    - iris>=3.5
+    - iris>=3.12.2 # https://github.com/SciTools/iris/issues/6417
     - cartopy>=0.20
     - hdf5!=1.12.2
-    - dask-core!=2025.4.0,!=2025.4.1