Add CI job to check for forgotten packaging

In order to allow beta testing, it is necessary to package the action after every change to the code. This is an easy
step to forget, so an automated check is necessary.

Author: per1234

.github/workflows/setup-taskflile.yml

@@ -29,3 +29,29 @@ jobs:
 
       - name: npm test
         run: npm test
+
+  check-packaging:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v2
+        with:
+          node-version: 12.x
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Build action
+        run: npm run build
+
+      - name: Package action
+        run: npm run pack
+
+      - name: Check packaging
+        # Ignoring CR because ncc's output has a mixture of line endings, while the repository should only contain
+        # Unix-style EOL.
+        run: git diff --ignore-cr-at-eol --color --exit-code dist