Fix wheel build failed

[weipeng1999]

when i try to build this package as a wheel for my system, i found that there is no submodules in final wheel file, that means the package only has 'init.py', in other words xskillscore.core, xskillscore.test and xskillscore.versioning are gone.
after some research, i found that it was because the item tool.setuptools.packages in pyproj.toml not be setted correctly, and I add a patch to build wheel successfully,
Please consider to merge the patch to fix wheel constrution:

diff --git a/pyproject.toml b/pyproject.toml
index 2ae2e11..9594ccb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -72,7 +72,7 @@ repository = "https://github.com/xarray-contrib/xskillscore"
 documentation = "https://xskillscore.readthedocs.io/en/stable/"
 
 [tool.setuptools]
-packages = ["xskillscore"]
+packages = ["xskillscore", "xskillscore.core", "xskillscore.versioning"]
 
 [tool.setuptools_scm]
 fallback_version = "9999"

besides, here is my build environment:

>>> pip list | grep -e "\(setuptools\|installer\|build\|wheel\)"                                                                      (base)
build                         1.2.1
installer                     0.7.0
setuptools                    69.5.1
setuptools-scm                8.1.0
wheel                         0.44.0