ci: validate maintainers also checks for duplicate maintainers

We dont want need to maintain duplicate entries for maintainers in HM
that already exist in Nixpkgs. Add a check that calls out users that
don't need an entry in our internal list.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

.github/workflows/validate-maintainers.yml

@@ -72,6 +72,49 @@ jobs:
             print('✅ All maintainer entries are valid')
             print(f'✅ Validated {len(maintainers)} maintainer entries')
           "
+      - name: Check for duplicate maintainers
+        run: |
+          echo "🔍 Checking for duplicate maintainers between HM and nixpkgs..."
+          python3 -c "
+          import json
+          import subprocess
+          import sys
+
+          hm_result = subprocess.run(['nix', 'eval', '--file', 'modules/lib/maintainers.nix', '--json'],
+                                    capture_output=True, text=True, check=True)
+          hm_maintainers = json.loads(hm_result.stdout)
+          hm_github_users = set()
+          for name, data in hm_maintainers.items():
+            if 'github' in data:
+              hm_github_users.add(data['github'])
+
+          nixpkgs_result = subprocess.run(['nix', 'eval', 'nixpkgs#lib.maintainers', '--json'],
+                                         capture_output=True, text=True, check=True)
+          nixpkgs_maintainers = json.loads(nixpkgs_result.stdout)
+          nixpkgs_github_users = set()
+          for name, data in nixpkgs_maintainers.items():
+            if isinstance(data, dict) and 'github' in data:
+              nixpkgs_github_users.add(data['github'])
+
+          duplicates = hm_github_users.intersection(nixpkgs_github_users)
+
+          if duplicates:
+            print(f'❌ Found {len(duplicates)} duplicate maintainers between HM and nixpkgs:')
+            for github_user in sorted(duplicates):
+              # Find the HM attribute name for this github user
+              hm_attr = None
+              for attr_name, data in hm_maintainers.items():
+                if data.get('github') == github_user:
+                  hm_attr = attr_name
+                  break
+              print(f'  - {github_user} (HM attribute: {hm_attr})')
+            print()
+            print('These maintainers should be removed from HM maintainers file to avoid duplication.')
+            print('They can be referenced directly from nixpkgs instead.')
+            sys.exit(1)
+          else:
+            print('✅ No duplicate maintainers found')
+          "
       - name: Test generation
         if: inputs.run_tests == true
         run: |