Add github workflow to proxy tests from sr.ht

.github/workflows/repo-lockdown.yml

@@ -0,0 +1,16 @@
+name: "Repo Lockdown"
+
+on:
+  pull_request_target:
+    types: 'opened'
+
+permissions:
+  pull-requests: write
+
+jobs:
+  action:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/repo-lockdown@v4
+        with:
+          pr-comment: "This repo does not accept pull requests as it is a mirror. Please instead submit patches to https://sr.ht/~bryan_bennett/flake_env."

.github/workflows/test.yml

@@ -0,0 +1,14 @@
+name: "Test"
+on:
+  pull_request:
+  push:
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v25
+      with:
+        github_access_token: ${{ secrets.GITHUB_TOKEN }}
+    - run: nix build
+    - run: nix flake check --all-systems --keep-going