Add CI for Stack (#457)

Author: BinderDavid

.github/workflows/stack-ci.yml

@@ -0,0 +1,29 @@
+name: Stack CI
+
+on:
+  push:
+    paths:
+      - 'message-index/site.hs'
+      - 'message-index/message-index.cabal'
+      - 'message-index/stack.yaml'
+      - 'message-index/stack.yaml.lock'
+    branches:
+      - main
+  pull_request:
+    paths:
+      - 'message-index/site.hs'
+      - 'message-index/message-index.cabal'
+      - 'message-index/stack.yaml'
+      - 'message-index/stack.yaml.lock'
+    branches:
+      - main
+
+jobs:
+  stack-ci:
+    name: Stack CI
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: freckle/stack-action@v4
+      with:
+        working-directory: message-index