gitaly: Copy gem files into bundler env instead of symlinking

This fixes issue #79374, where gitaly prints warning messages on the
client side when running push or fetch.

pkgs/applications/version-management/gitlab/gitaly/default.nix

@@ -5,6 +5,7 @@ let
   rubyEnv = bundlerEnv rec {
     name = "gitaly-env";
     inherit ruby;
+    copyGemFiles = true;
     gemdir = ./.;
     gemset =
       let x = import (gemdir + "/gemset.nix");