Maintainers: Update Nullcube (#381372)

Author: wegank

maintainers/maintainer-list.nix

@@ -16998,7 +16998,7 @@
   nullcube = {
     email = "[email protected]";
     name = "NullCube";
-    github = "nullcub3";
+    github = "nullcubee";
     githubId = 51034487;
     matrix = "@nullcube:matrix.org";
   };