unittest.mock doc: Fix references to recursive seal of Mocks (GH-9028)


The docs in `library/unittest.mock` have been updated to remove
confusing terms about submock and be explicit about the behavior
expected.
(cherry picked from commit 96200eb2ffcda05de14099cf23f60d5091366e3e)

Co-authored-by: Mario Corchero <mariocj89@gmail.com>
diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index cfc0d76..1a6c251 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -2423,15 +2423,14 @@
 
 
 def seal(mock):
-    """Disable the automatic generation of "submocks"
+    """Disable the automatic generation of child mocks.
 
     Given an input Mock, seals it to ensure no further mocks will be generated
     when accessing an attribute that was not already defined.
 
-    Submocks are defined as all mocks which were created DIRECTLY from the
-    parent. If a mock is assigned to an attribute of an existing mock,
-    it is not considered a submock.
-
+    The operation recursively seals the mock passed in, meaning that
+    the mock itself, any mocks generated by accessing one of its attributes,
+    and all assigned mocks without a name or spec will be sealed.
     """
     mock._mock_sealed = True
     for attr in dir(mock):