refactor(grfn): Prepare for restricted-eval

Change-Id: I672ad0898b2ef6a11f8bc9233da0ded4a296fe0e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5686
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

users/grfn/system/home/modules/common.nix

@@ -13,6 +13,7 @@
     ../modules/lib/cloneRepo.nix
   ];
 
+  home.username = "grfn";
   home.homeDirectory = "/home/grfn";
 
   programs.password-store.enable = true;