Add lysnikolaou to CODEOWNERS for the new parser (GH-21252)

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index c33bf1e..31003a8 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -73,9 +73,9 @@
 /Doc/library/gc.rst           @pablogsal
 
 # Parser
-/Parser/                      @pablogsal
-/Tools/peg_generator/         @pablogsal
-/Lib/test/test_peg_generator/ @pablogsal
+/Parser/                      @pablogsal @lysnikolaou
+/Tools/peg_generator/         @pablogsal @lysnikolaou
+/Lib/test/test_peg_generator/ @pablogsal @lysnikolaou
 
 # SQLite 3
 **/*sqlite*                   @berkerpeksag