Restore explicit discovery, fixing the build.

setup.cfg

@@ -19,15 +19,20 @@ classifiers =
 keywords = CSS, Cascading Style Sheets, CSSParser, DOM Level 2 Stylesheets, DOM Level 2 CSS
 
 [options]
+packages = find_namespace:
 include_package_data = true
 python_requires = >=3.8
 install_requires =
 	importlib_metadata; python_version < "3.8"
 
 [options.packages.find]
 exclude =
+    # duplicate exclusions for pypa/setuptools#2688
+	docs
+	docs.*
 	examples*
-	sheets*
+	sheets
+	sheets.*
 	tools*
 
 [options.extras_require]