I need to work with the C# scripting and for that I need to get the mono version

Nobody has claimed this yet.

# Problem
So I am pretty new to Nixos, got it a few days ago. And I wanted to start working on my Godot game on it, I couldn't find the version I needed 4.2.1, until I found your work.
Works perfectly, but it only work with GDscript and I want to use C# (my code is already in C# and I want to get better at C#).
I tried just quickly changing the pkgs.fetchurl and adding dependencies, and it start building, but fails because of dependencies (I think).
# Here is what I did in detail:
## new pkgs.fetchurl
```nix
godot-stable = pkgs.fetchurl {
url = "https://github.com/godotengine/godot/releases/download/${version}-stable_mono/Godot_v${version}-stable_mono_linux.x86_64.zip";
hash = "sha256-hjEannW3RF60IVMS5gTfH2nHLUZBrz5nBJ4wNWrjdmA=";
};

```

## Dependenci I added
```nix
pkgs.dotnet-sdk_8
pkgs.dotnetCorePackages.runtime_8_0
pkgs.dotnetCorePackages.sdk_8_0
pkgs.xorg.libX11
pkgs.godot3-mono
```
Even added godot3-mono because they probably have similar dependency, and went testing it does work normally on my machine with the other dependencies.
There is maybe something else I should modifie to get it work. But it did seem to be building, but failed and I god this error:
## Error message
```shell
warning: Git tree '/home/samuel/Documents/Godot/godot-flake' is dirty
error: builder for '/nix/store/jsdqfh8g2jgwbh22ax8flwwcns2klsy4-Godot_v4.2.1-stable_mono_linux.x86_64.zip.drv' failed with exit code 1;
last 7 log lines:
>
> trying https://github.com/godotengine/godot/releases/download/4.2.1-stable_mono/Godot_v4.2.1-stable_mono_linux.x86_64.zip
> % Total % Received % Xferd Average Speed Time Time Time Current
> Dload Upload Total Spent Left Speed
> 0 9 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
> curl: (22) The requested URL returned error: 404
> error: cannot download Godot_v4.2.1-stable_mono_linux.x86_64.zip from any mirror
For full logs, run 'nix log /nix/store/jsdqfh8g2jgwbh22ax8flwwcns2klsy4-Godot_v4.2.1-stable_mono_linux.x86_64.zip.drv'.
error: 1 dependencies of derivation '/nix/store/jjf7sa7vndwyjdm0awd1r041v2qhkhbq-godot-4.2.1.drv' failed to build
error: 1 dependencies of derivation '/nix/store/nzscbjhkknddwvlg65miak0qxdxcgfks-godot-usr-target.drv' failed to build
error: 1 dependencies of derivation '/nix/store/2pa2cd57izbkp0zb1l6d3swcvvva2b8l-godot-fhs.drv' failed to build
error: 1 dependencies of derivation '/nix/store/kj8d6rdwyvyivs72yw4qgwnyb68h49sp-godot-bwrap.drv' failed to build
error: 1 dependencies of derivation '/nix/store/5bszhj0gd10p1mga3fc9f0xska3aa18d-godot.drv' failed to build
error: 1 dependencies of derivation '/nix/store/95nnb8pc3bj5dzk4fhahpcb193x6435x-nix-shell-env.drv' failed to build

```

# Personal Conclusion
But I feel like I could use a second opinion, and if fixed maybe we can add an option to get the godot with .net working as easily as with just GDscript.
PS: my first Issues post on github, open to feedback if I did something wrong or info is missing.

Start with the Godot 4.2.1 derivation and its pkgs.fetchurl definition, checking the requested Mono release URL and the listed .NET dependencies. Done means the flake builds a Godot 4.2.1 C#/.NET variant successfully and makes it available as easily as the existing GDScript package.

Written by the indexing model from the issue text.