Fix xarray merge compat FutureWarning

[aladinor]

Add explicit compat='override' parameter to xr.merge() call in _get_subgroup function to silence FutureWarning about upcoming xarray default changes.

• Closes FutureWarning: In a future version of xarray the default value for compat will change from compat='no_conflicts' to compat='override' #313
• Changes are documented in history.md

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.50%. Comparing base (93c33ea) to head (bdba528).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #314   +/-   ##
=======================================
  Coverage   93.50%   93.50%           
=======================================
  Files          27       27           
  Lines        5587     5587           
=======================================
  Hits         5224     5224           
  Misses        363      363           

Flag	Coverage Δ
notebooktests	?
unittests	93.50% <100.00%> (ø)

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[egouden]

There are still future warnings related to merge.

[kmuehlbauer]

@aladinor @egouden I've pushed a fix for the remaining xr.merge in cfradial1 backend.

[kmuehlbauer]

Thanks @aladinor!

[egouden]

Great! Thanks.