[3.12] Docs: fix markup for importlib.machinery.NamespaceLoader (GH-112479) (#112481)

Docs: fix markup for `importlib.machinery.NamespaceLoader` (GH-112479)
(cherry picked from commit 2e632fa)

Co-authored-by: Alex Waygood <[email protected]>

Author: miss-islington

Doc/library/importlib.rst

@@ -1145,7 +1145,7 @@ find and load modules.
       .. versionadded:: 3.4
 
 
-.. class:: NamespaceLoader(name, path, path_finder):
+.. class:: NamespaceLoader(name, path, path_finder)
 
    A concrete implementation of :class:`importlib.abc.InspectLoader` for
    namespace packages.  This is an alias for a private class and is only made