age: skip flaky plugin test

See issue in upstream FiloSottile/age#517.
age fails this test on both x86_64 and aarch64, but sometimes it doesn't.
Disable this test until the upstream issue is resolved.

pkgs/tools/security/age/default.nix

@@ -1,4 +1,4 @@
-{ lib, buildGoModule, fetchFromGitHub, fetchpatch, installShellFiles }:
+{ lib, buildGoModule, fetchFromGitHub, fetchpatch, installShellFiles, stdenv }:
 
 buildGoModule rec {
   pname = "age";
@@ -53,6 +53,11 @@ buildGoModule rec {
     fi
   '';
 
+  # plugin test is flaky on darwin, see https://github.com/FiloSottile/age/issues/517
+  preCheck = lib.optionalString stdenv.isDarwin ''
+    buildFlagsArray+=("-skip" "TestScript/plugin")
+  '';
+
   meta = with lib; {
     homepage = "https://age-encryption.org/";
     description = "Modern encryption tool with small explicit keys";