Address scalar/dimension concatenation error (#1780)

### What kind of change does this PR introduce?

* Fixes a previously uncaught error where remnants of a scenario
selection were not being dropped properly.

### Does this PR introduce a breaking change?

No.

CHANGES.rst

@@ -37,6 +37,7 @@ Internal changes
 Bug fixes
 ^^^^^^^^^
 * ``xclim.indices.{cold|hot}_spell_total_length`` now properly uses the argument `window` to only count spells with at least `window` time steps. (:issue:`1765`, :pull:`1777`).
+* Addressed an error in ``xclim.ensembles._filters._concat_hist`` where remnants of a scenario selection were not being dropped properly. (:pull:`1780`).
 
 v0.49.0 (2024-05-02)
 --------------------

tests/test_partitioning.py

@@ -1,24 +1,14 @@
 from __future__ import annotations
 
-import warnings
-
 import numpy as np
-import pytest
 import xarray as xr
-from packaging.version import Version
 
 from xclim.ensembles import fractional_uncertainty, hawkins_sutton, lafferty_sriver
 from xclim.ensembles._filters import _concat_hist, _model_in_all_scens, _single_member
 
 
-# FIXME: Investigate why _concat_hist() fails on xarray 2024.5.0
 def test_hawkins_sutton_smoke(open_dataset):
     """Just a smoke test."""
-    if Version(xr.__version__) == Version("2024.5.0"):
-        pytest.skip("xarray 2024.5.0 does not support `_concat_hist()` here.")
-    if Version(xr.__version__) > Version("2024.5.0"):
-        warnings.warn("FIXME: Remove this warning if this test is passing.")
-
     dims = {"run": "member", "scen": "scenario"}
     da = (
         open_dataset("uncertainty_partitioning/cmip5_pr_global_mon.nc")

xclim/ensembles/_filters.py

@@ -50,7 +50,7 @@ def _concat_hist(da: xr.DataArray, **hist) -> xr.DataArray:
     ((dim, _),) = hist.items()
 
     # Select historical scenario and drop it from the data
-    h = da.sel(**hist).dropna("time", how="all")
+    h = da.sel(drop=True, **hist).dropna("time", how="all")
     ens = da.drop_sel(**hist)
 
     index = ens[dim]