chore: reduce warnings related to system

Current system value has been moved into `pkgs.stdenv.hostPlatform` by NixOS/nixpkgs#456527

Author: jfroche

nix/cargo-pgrx/mkPgrxExtension.nix

@@ -4,6 +4,7 @@
   pgrxVersion,
   makeRustPlatform,
   rust-bin,
+  stdenv,
   system,
 }:
 let
@@ -42,7 +43,7 @@ let
           import (builtins.fetchTarball {
             url = "https://channels.nixos.org/nixos-22.11/nixexprs.tar.xz";
             sha256 = "1j7h75a9hwkkm97jicky5rhvzkdwxsv5v46473rl6agvq2sj97y1";
-          }) { inherit system; }
+          }) { inherit (stdenv.hostPlatform) system; }
         );
       in
       rustPlatform.bindgenHook.overrideAttrs {

nix/overlays/default.nix

@@ -6,7 +6,7 @@
     # want to have an arbitrary order, since it might matter. being
     # explicit is better.
 
-    inherit (self.packages.${final.system})
+    inherit (self.packages.${final.stdenv.hostPlatform.system})
       postgresql_15
       postgresql_17
       postgresql_orioledb-17

nix/packages/default.nix

@@ -48,7 +48,7 @@
           migrate-tool = pkgs.callPackage ./migrate-tool.nix { psql_15 = self'.packages."psql_15/bin"; };
           overlayfs-on-package = pkgs.callPackage ./overlayfs-on-package.nix { };
           packer = pkgs.callPackage ./packer.nix { inherit inputs; };
-          pg-backrest = inputs.nixpkgs.legacyPackages.${pkgs.system}.pgbackrest;
+          pg-backrest = inputs.nixpkgs.legacyPackages.${pkgs.stdenv.hostPlatform.system}.pgbackrest;
           pg-restore = pkgs.callPackage ./pg-restore.nix { psql_15 = self'.packages."psql_15/bin"; };
           pg_prove = pkgs.perlPackages.TAPParserSourceHandlerpgTAP;
           pg_regress = makePgRegress activeVersion;

nix/postgresql/generic.nix

@@ -322,15 +322,15 @@ let
 
           tests = {
             postgresql-wal-receiver = import ../../../../nixos/tests/postgresql-wal-receiver.nix {
-              inherit (stdenv) system;
+              inherit (stdenv.hostPlatform) system;
               pkgs = self;
               package = this;
             };
             pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
           }
           // lib.optionalAttrs jitSupport {
             postgresql-jit = import ../../../../nixos/tests/postgresql-jit.nix {
-              inherit (stdenv) system;
+              inherit (stdenv.hostPlatform) system;
               pkgs = self;
               package = this;
             };