ci: generate-all-maintainers use nix eval update

Previously, we had to hack together some string matching to identify and
retrieve the maintainers in the repo. We can just eval the modules to
retrieve the list of maintainers more accurately.

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

.github/workflows/update-maintainers.yml

@@ -59,6 +59,8 @@ jobs:
         run: |
           echo "📋 Generating updated all-maintainers.nix..."
           ./lib/python/generate-all-maintainers.py
+          echo "🎨 Formatting with nixfmt..."
+          nix fmt all-maintainers.nix
       - name: Check for changes
         id: check-changes
         run: |