Update CODEOWNERS

MLIR and Swift SIG owners.

Author: Edd Wilder-James

CODEOWNERS

@@ -13,6 +13,8 @@ sigs/networking/ @martinwicke @ewilderj @byronyi @jbedorf @poxvoculi
 sigs/io/ @martinwicke @ewilderj @mrry @yongtang @dmitrievanthony
 sigs/jvm/ @martinwicke @ewilderj @sjamesr @karllessard @tzolov
 sigs/micro/ @martinwicke @ewilderj @petewarden
+sigs/mlir/ @ewilderj @pkanwar23
+sigs/swift/ @ewilderj @saeta @dynamicwebpaige
 sigs/testing/ @ewilderj @dynamicwebpaige
 
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