tests: add check for nixpkgs maintainers

The test fails if a nixvim maintainer is also a nixpkgs maintainer.

flake-modules/tests.nix

@@ -44,6 +44,8 @@
           inherit pkgs helpers;
           inherit (pkgs) lib;
         };
+
+        maintainers = import ../tests/maintainers.nix { inherit pkgs; };
       };
     };
 }

tests/maintainers.nix

@@ -0,0 +1,21 @@
+{
+  pkgs ? import <nixpkgs> { },
+  lib ? pkgs.lib,
+}:
+let
+  inherit (lib) attrNames filter length;
+  nixvimList = import ../lib/maintainers.nix;
+  nixpkgsList = lib.maintainers;
+  duplicates = filter (name: nixpkgsList ? ${name}) (attrNames nixvimList);
+  count = length duplicates;
+in
+pkgs.runCommand "maintainers-test" { inherit count duplicates; } ''
+  if [ $count -gt 0 ]; then
+    echo "$count nixvim maintainers are also nixpkgs maintainers:"
+    for name in $duplicates; do
+      echo "- $name"
+    done
+    exit 1
+  fi
+  touch $out
+''