Add flake.yaml CI

.forgejo/workflows/flake.yaml

@@ -0,0 +1,14 @@
+name: Flake Test
+on:
+  push:
+    branches:
+      - main
+jobs:
+  check:
+    runs-on: self-hosted
+    steps:
+      - uses: actions/checkout@v3
+      - name: Run `nix flake show`
+        run: nix flake show
+      - name: Run `nix flake check`
+        run: nix flake check