Require sphinx>=4.2 (cleanup) (#421)

Author: jarrodmillman

numpydoc/numpydoc.py

@@ -30,8 +30,8 @@
 from sphinx.util import logging
 from sphinx.errors import ExtensionError
 
-if sphinx.__version__ < "3.0":
-    raise RuntimeError("Sphinx 3.0 or newer is required")
+if sphinx.__version__ < "4.2":
+    raise RuntimeError("Sphinx 4.2 or newer is required")
 
 from .docscrape_sphinx import get_doc_object
 from .validate import validate, ERROR_MSGS