Add a CI check for the CI source files

Check on the CI that the (generated) CI config files do match their
Nickel source.

Not as nice as a really dynamic CI, but at least makes sure that things
don't drift apart

.github/workflows/check-up-to-date-generated-files.yml

@@ -0,0 +1,20 @@
+jobs:
+  check-up-to-date-generated-files:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+    - name: Install Nix
+      uses: cachix/install-nix-action@v26
+      with:
+        extra_nix_config: accept-flake-config = true
+    - uses: cachix/cachix-action@v14
+      with:
+        authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
+        name: nickel-schemastore
+    - name: Check that the file generated by Organist are up-to-date
+      run: |-
+        nix run .#regenerate-files -L
+        git diff --exit-code && echo "All files up-to-date ✅"
+on:
+  push: {}

gh-actions.ncl

@@ -67,4 +67,22 @@ in
     on.schedule = [{ cron = "0 0 * * 0" }],
     on.workflow_dispatch = {},
   },
+
+  check-up-to-date-generated-files = {
+    on.push = {},
+    jobs.check-up-to-date-generated-files = {
+      runs-on = "ubuntu-latest",
+      steps =
+        setup
+        @ [
+          {
+            name = "Check that the file generated by Organist are up-to-date",
+            run = m%"
+              nix run .#regenerate-files -L
+              git diff --exit-code && echo "All files up-to-date ✅"
+            "%
+          }
+        ],
+    },
+  },
 } | { _ | gha }