maintainers: add takagiy

maintainers/maintainer-list.nix

···
     githubId = 321799;
     name = "Paul Colomiets";
   };
+  takagiy = {
+    email = "[e-mail]";
+    github = "takagiy";
+    githubId = 18656090;
+    name = "Yuki Takagi";
+  };
   taketwo = {
     email = "[e-mail]";
     github = "taketwo";