[GitHub] [NFC] Add moxinilian to IRDL CODEOWNERS (llvm#159135)

This is so I get notified when an IRDL file is updated.

Author: Moxinilian

.github/CODEOWNERS

@@ -132,6 +132,9 @@
 /mlir/**/Transforms/Mem2Reg.* @moxinilian
 /mlir/**/Transforms/SROA.* @moxinilian
 
+# MLIR IRDL-related
+/mlir/**/*IRDL* @moxinilian
+
 # BOLT
 /bolt/ @aaupov @maksfb @rafaelauler @ayermolo @yota9 @paschalis-mpeis @yozhu