...and try using a different workflow file??

.github/workflows/main.yml

@@ -0,0 +1,27 @@
+name: Eleventy Build
+
+on:
+  push:
+    branches:
+      - main
+      
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup Node
+        uses: actions/setup-node@v1
+        with:
+          node-version: '16.x'
+
+      - run: npm ci
+
+      - run: npm run build
+
+      - name: Deploy
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          deploy_key: ${{ secrets.ACTIONS_DEPLOY_KEY }}
+          publish_dir: ./pub