nix-bash-completions: Reduce priority for Nix 2.4

Reducing the priority makes the system build prefer the Nix-provided
completions, for e.g. the new `nix` commands.

pkgs/shells/bash/nix-bash-completions/default.nix

@@ -32,5 +32,7 @@ stdenv.mkDerivation rec {
     license = licenses.bsd3;
     platforms = platforms.all;
     maintainers = with maintainers; [ hedning ];
+    # Set a lower priority such that the newly provided completion from Nix 2.4 are preferred.
+    priority = 10;
   };
 }