fix workflow syntax

Author: thomas loubrieu

.github/workflows/sync_labels.yaml

@@ -11,9 +11,8 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: micnncim/action-label-syncer@v1
-        with:
-          prune: false
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
-          manifest: path/to/manifest/labels.yml
+          manifest: labels.yml
+          with.prune: false