Switch to using the netdatabot access token for actions. (#7697)

This updates the access token in the labeler action to use permissions
of the netdatabot account instead of using the generic access token
provided by GitHub.

This allows the labeling to work correctly even for forks owned by
people who do not have write access to the repo.

.github/workflows/labeler.yml

@@ -14,4 +14,4 @@ jobs:
     steps:
       - uses: actions/labeler@v2
         with:
-          repo-token: "${{ secrets.GITHUB_TOKEN }}"
+          repo-token: "${{ secrets.NETDATABOT_TOKEN }}"