test(grafana): Use older nixpkgs for grafana on macOS

This speeds up build, because we no longer have to compile grafana locally and wait for eternity.

cf. NixOS/nixpkgs#273998

test/flake.nix

@@ -5,19 +5,23 @@
     systems.url = "github:nix-systems/default";
     process-compose-flake.url = "github:Platonic-Systems/process-compose-flake";
     services-flake = { };
+
+    # Deal with broken packages:
+    # grafana is broken on aarch64-darwin: https://github.com/NixOS/nixpkgs/issues/273998
+    nixpkgs-grafana.url = "github:nixos/nixpkgs/b604023e0a5549b65da3040a07d2beb29ac9fc63";
   };
   outputs = inputs:
     inputs.flake-parts.lib.mkFlake { inherit inputs; } {
       systems = import inputs.systems;
       imports = [
         inputs.process-compose-flake.flakeModule
       ];
-      perSystem = { self', pkgs, system, lib, ... }: {
+      perSystem = { self', inputs', pkgs, system, lib, ... }: {
         _module.args.pkgs = import inputs.nixpkgs {
           inherit system;
           # Required for elastic search
           config.allowUnfree = true;
-          overlays = import ./overlays { inherit system lib; };
+          overlays = import ./overlays { inherit system inputs' lib; };
         };
         process-compose =
           let

test/overlays/default.nix

@@ -1,11 +1,13 @@
-{ lib, system, ... }:
+{ inputs', lib, system, ... }:
 
 let
   isDarwin = system == "x86_64-darwin" || system == "aarch64-darwin";
 in
 lib.optionals isDarwin [
   (import ./pgadmin.nix)
-  (import ./grafana.nix)
+  (self: super: {
+    grafana = inputs'.nixpkgs-grafana.legacyPackages.grafana;
+  })
 ]
 ++
 [