clanServices: Move ergochat test to appropriate location

Move the ergochat clanService test to the ergochat clan service.
The tests should live close to the definition of the service, so that
debugging and discoverability is better.

clanServices/ergochat/flake-module.nix

@@ -1,6 +1,17 @@
-{ lib, ... }:
+{ lib, self, ... }:
 {
   clan.modules = {
     ergochat = lib.modules.importApply ./default.nix { };
   };
+  perSystem =
+    { pkgs, ... }:
+    {
+      checks = lib.optionalAttrs (pkgs.stdenv.isLinux) {
+        ergochat = import ./tests/vm/default.nix {
+          inherit pkgs;
+          clan-core = self;
+          nixosLib = import (self.inputs.nixpkgs + "/nixos/lib") { };
+        };
+      };
+    };
 }