Correct trivial grammar in reset_mock docs (pythonGH-101861)

(cherry picked from commit a1f08f5)

Co-authored-by: Steve Kowalik <steven@wedontsleep.org>

Doc/library/unittest.mock.rst

@@ -406,7 +406,7 @@ the *new_callable* argument to :func:`patch`.
             False
 
         .. versionchanged:: 3.6
-           Added two keyword only argument to the reset_mock function.
+           Added two keyword-only arguments to the reset_mock function.
 
         This can be useful where you want to make a series of assertions that
         reuse the same object. Note that :meth:`reset_mock` *doesn't* clear the
@@ -416,8 +416,8 @@ the *new_callable* argument to :func:`patch`.
         parameter as ``True``. Child mocks and the return value mock
         (if any) are reset as well.
 
-        .. note:: *return_value*, and :attr:`side_effect` are keyword only
-                  argument.
+        .. note:: *return_value*, and :attr:`side_effect` are keyword-only
+                  arguments.
 
 
     .. method:: mock_add_spec(spec, spec_set=False)