ci: cache ndg builds after checks

Author: horriblename

.github/workflows/check.yml

@@ -100,6 +100,13 @@ jobs:
             substituters = https://cache.nixos.org/ https://feel-co.cachix.org
             trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= feel-co.cachix.org-1:nwEFNnwZvtl4KKSH5LDg+/+K7bV0vcs6faMHAJ6xx0w=
 
+      - uses: cachix/cachix-action@v16
+        with:
+          authToken: ${{ secrets.CACHIX_TOKEN }}
+          extraPullNames: nix-community
+          name: nvf
+          pushFilter: '(ndg-\d+\.\d+\.\d+$)'
+
       - name: Set default git branch (to reduce log spam)
         run: git config --global init.defaultBranch main