treewide: xvfb_run -> xvfb-run

[roberth]

Motivation for this change

Consistency.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[SuperSandro2000]

Did you use ripgrep to double check that you didn't miss something that is not always evaluated?

[fricklerhandwerk]

I checked. Nothing left. Alias is in place.

[roberth]

Did you use ripgrep to double check that you didn't miss something that is not always evaluated?

Yes.

• Semi-automated find and replace with vscode
• git add --patch
• git show -U0 --word-diff --word-diff-regex=. to check
• ofborg

I'll merge this after ofborg, to avoid another merge conflict.