Add Mark Shannon to CODEOWNERS. (#22914)

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 5b8662c..8c76f54 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -9,10 +9,16 @@
 
 # Core
 **/*context*                  @1st1
-**/*genobject*                @1st1
+**/*genobject*                @1st1 @markshannon
 **/*hamt*                     @1st1
 Objects/set*                  @rhettinger
-Objects/dict*                 @methane
+Objects/dict*                 @methane @markshannon
+Objects/type*                 @markshannon
+Objects/codeobject.c          @markshannon
+Objects/frameobject.c         @markshannon
+Objects/call.c                @markshannon
+Python/ceval.c                @markshannon
+Python/compile.c              @markshannon
 
 # Hashing
 **/*hashlib*                  @python/crypto-team @tiran