Disabled users.mutableUsers conflicts with mutable overlay-based /etc

[ivan770]

Describe the bug

The following assertion triggers in a configuration where users.mutableUsers = false; and system.etc.overlay.mutable = true;:

nixpkgs/nixos/modules/system/etc/etc-activation.nix

Lines 29 to 35 in ee188fb

	{
	assertion = config.systemd.sysusers.enable -> (config.users.mutableUsers == config.system.etc.overlay.mutable);
	message = ''
	When using systemd-sysusers and mounting `/etc` via an overlay, users
	can only be mutable when `/etc` is mutable and vice versa.
	'';
	}

It should be possible to have a mutable /etc while using static systemd-sysusers configuration at the same time.

Steps To Reproduce

Steps to reproduce the behavior:

1. Set users.mutableUsers to false
2. Set system.etc.overlay.mutable to true
3. Build the system

Expected behavior

The build succeeds.

Notify maintainers

From git blame: @nikstur

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

 - system: `"x86_64-linux"`
 - host os: `Linux 6.8.9, NixOS, 24.05 (Uakari), 24.05.20240513.cbd6db0`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.22.0`
 - nixpkgs: `/etc/nix/inputs/nixpkgs`

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[nikstur]

This cannot be done with the current implementation.