supress namespace_package deprecation warning (doctests) (#7548)

Author: mathause

xarray/tests/__init__.py

@@ -37,6 +37,7 @@
 
 # https://github.com/pydata/xarray/issues/7322
 warnings.filterwarnings("ignore", "'urllib3.contrib.pyopenssl' module is deprecated")
+warnings.filterwarnings("ignore", "Deprecated call to `pkg_resources.declare_namespace")
 
 arm_xfail = pytest.mark.xfail(
     platform.machine() == "aarch64" or "arm" in platform.machine(),