CI: also run hlint

Author: m4lvin

.github/workflows/lint.yml

@@ -0,0 +1,21 @@
+name: lint
+on:
+  pull_request:
+  push:
+
+jobs:
+  hlint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v6
+
+    - name: 'Set up HLint'
+      uses: haskell-actions/hlint-setup@v2
+      with:
+        version: '3.10'
+
+    - name: 'Run HLint'
+      uses: haskell-actions/hlint-run@v2
+      with:
+        path: '["lib/", "test/", "exec/"]'
+        fail-on: warning