Motivation for this change

I got this error when building fsharp41:
/private/var/folders/.../nix-build-fsharp-4.1.34.drv-0/fsharp-4.1.34/src/scripts/fssrgen.fsx(334,28) : error FS0041: A unique overload for method 'GetFileNameWithoutExtension' could not be determined based on type information prior to this program point. A type annotation may be needed. Candidates: System.IO.Path.GetFileNameWithoutExtension(path: System.ReadOnlySpan< char>) : System.ReadOnlySpan<char>, System.IO.Path.GetFileNameWithoutExtension(path: string) : string (...)

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.