diskoLib.vmToolsSupportsCustomQemu might test incorrect field

[RadxaYuntian]

Introduced in #851, diskoLib.vmToolsSupportsCustomQemu is used to check if the current nixpkgs supports overriding QEMU package.

While disko in general should be used with nixos-unstable, due to #900 I'm current targetting nixos-24.11. With the following test project I got the following error:

       error:
       Failed assertions:
       - You have set config.disko.imageBuild.qemu, but vmTools in your nixpkgs version "24.11.20241123.0c58267"
       does not support overriding the qemu package with the customQemu option yet.
       Please upgrade nixpkgs so that `lib.version` is at least "24.11.20240709".

Here is the table for the tested combinations:

	nixos-24.11	nixos-unstable
diskoImages	This issue	OK
diskoImagesScript	This issue	#900

Checking lib.versionAtLeast "24.11.20241123.0c58267" "24.11.20240709" in nix repl got the expected True. After checking the source I found out that the assert is printing lib.version but vmToolsSupportsCustomQemu is checking pkgs.lib.version. I updated the assert message and the error now makes more sense:

       error:
       Failed assertions:
       - You have set config.disko.imageBuild.qemu, but vmTools in your nixpkgs version "24.11pre-git"
       does not support overriding the qemu package with the customQemu option yet.
       Please upgrade nixpkgs so that `lib.version` is at least "24.11.20240709".

I think we should change vmToolsSupportsCustomQemu to check lib.version as well, because that value looks to be more correct, but I know little between the difference of those 2 fields and how they actually should be used.

[RadxaYuntian]

Ping @iFreilicht who is the author of the original check.

[iFreilicht]

Can confirm. I looked into what could be causing the issue, and encountered something weird. I've downloaded your example flake, and it seems the pkgs that arrives in the configuration is different from the flake's input:

$ nix repl 
Lix 2.91.1
Type :? for help.
nix-repl> :lf .
Added 9 variables.

nix-repl> inputs.nixpkgs.lib.version
"24.11.20241123.0c58267"

nix-repl> inputs.nixpkgs.legacyPackages.x86_64-linux.lib.version
"24.11.20241123.0c58267"

nix-repl> inputs.disko.inputs.nixpkgs.lib.version
"24.11.20241123.0c58267"

nix-repl> nixosConfigurations.test.pkgs.lib.version
"24.11pre-git"

nix-repl> nixosConfigurations.test.config.disko.imageBuilder.pkgs.lib.version
"24.11pre-git

Either way, the solution is as you say, just use lib instead of pkgs.lib. Fix is in #906