ci: labeler: Use actions/labeler@v4

This commit updates the labeler workflow to use the labeler action v4,
which is based on node.js 16 and @actions/core 1.10.0, in preparation
for the upcoming removal of the deprecated GitHub features.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

.github/workflows/labeler.yml

@@ -7,4 +7,4 @@ jobs:
     name: Pull Request Labeler
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/labeler@v2.1.1
+      - uses: actions/labeler@v4