Merge PR #255 (Peg xarray to 2023.2.0 in environment.yml)

This merge brings PR #255 (Peg xarray to version 2023.2.0 in the
environment.yml file, by @yantosca) into the GCPy 1.4.0 development
stream.

We have chosen to revert xarray to the 2023.2.0 version in order to
avoid some xarray/dask shenanigans that break backwards compatibility
with benchmark plotting code.  We can revert to the latest xarray
once what code updates in GCPy are necessary.

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

docs/environment_files/environment.yml

@@ -35,7 +35,13 @@ dependencies:
     - scipy                           # Scientific python package
     - sparselt>=0.1.3                 # Regridding earth system model data
     - tabulate                        # Pretty-printing for column data
-    - xarray                          # Read data from netCDF etc files
+    #
+    # NOTE: The most recent xarray (2023.8.0) seems to break backwards
+    # compatibility with the benchmark plotting code.  Peg to 2023.2.0
+    # until we can update GCPy for the most recent xarray.
+    #  -- Bob Yantosca (29 Aug 2023)
+    #
+    - xarray==2023.2.0                # Read data from netCDF etc files
     #
     # NOTE: These packages need to be pegged at specific versions
     # in order to avoid an ImportError.