fix(pg_stat_monitor): use pkgs.testers.runNixOSTest instead of self.inputs.nixpkgs.lib.nixos.runTest

The pg_stat_monitor test was using self.inputs.nixpkgs.lib.nixos.runTest
with hostPkgs parameter, which causes cross-compilation issues on Darwin
when building Linux VMs. This change aligns it with all other extension
tests by using pkgs.testers.runNixOSTest, which properly handles
cross-platform builds.

Author: yvan-sraka

nix/ext/tests/pg_stat_monitor.nix

@@ -70,9 +70,8 @@ let
   psql_15 = postgresqlWithExtension self.packages.${pkgs.stdenv.hostPlatform.system}.postgresql_15;
   psql_17 = postgresqlWithExtension self.packages.${pkgs.stdenv.hostPlatform.system}.postgresql_17;
 in
-self.inputs.nixpkgs.lib.nixos.runTest {
+pkgs.testers.runNixOSTest {
   name = pname;
-  hostPkgs = pkgs;
   nodes.server =
     { config, ... }:
     {