try and get a peak at mock-related PRs before they land (#25356)

.github/CODEOWNERS

@@ -91,6 +91,10 @@
 Parser/asdl_c.py              @isidentical
 Lib/ast.py                    @isidentical
 
+# Mock
+/Lib/unittest/mock.py         @cjw296
+/Lib/unittest/test/testmock/* @cjw296
+
 # SQLite 3
 **/*sqlite*                   @berkerpeksag