kopia: add blenderfreaky and nadir-ishiguro as maintainers

pkgs/by-name/ko/kopia/package.nix

···
     description = "Cross-platform backup tool with fast, incremental backups, client-side end-to-end encryption, compression and data deduplication";
     mainProgram = "kopia";
     license = lib.licenses.asl20;
-    maintainers = with lib; [ maintainers.bbigras ];
+    maintainers = with lib.maintainers; [
+      bbigras
+      blenderfreaky
+      nadir-ishiguro
+    ];
   };
 }