gh-92994: Clarify importlib "check" example (GH-92995)

Fixes GH-92994
(cherry picked from commit e39cd76)

Co-authored-by: Shantanu <[email protected]>

Author: miss-islington

Doc/library/importlib.rst

@@ -1250,6 +1250,9 @@ Checking if a module can be imported
 
 If you need to find out if a module can be imported without actually doing the
 import, then you should use :func:`importlib.util.find_spec`.
+
+Note that if ``name`` is a submodule (contains a dot),
+:func:`importlib.util.find_spec` will import the parent module.
 ::
 
   import importlib.util