feat(ci): Add Forgejo actions

.forgejo/workflows/check.yaml

@@ -0,0 +1,17 @@
+name: Check
+
+on:
+  push:
+    branches: ['master']
+
+jobs:
+  check:
+    runs-on: ubuntu-latest-amd64
+    steps:
+    - uses: actions/checkout@v3
+    - name: Check Flake
+      uses: https://github.com/DeterminateSystems/flake-checker-action@v5
+      with:
+        send-statistics: false
+    - name: Install Nix
+      uses: https://github.com/DeterminateSystems/nix-installer-action@v4