ci: use RENOVATE_TOKEN for Renovate to enable vulnerability alert access

The default GITHUB_TOKEN cannot read Dependabot/vulnerability alerts,
causing 'Cannot access vulnerability alerts' on the Dependency Dashboard.
Switch to the RENOVATE_TOKEN secret which can be granted alert read access.

Author: clavery

.github/workflows/renovate.yml

@@ -29,7 +29,7 @@ jobs:
         uses: renovatebot/github-action@v46.1.6
         with:
           configurationFile: renovate.json
-          token: ${{ secrets.GITHUB_TOKEN }}
+          token: ${{ secrets.RENOVATE_TOKEN }}
         env:
           LOG_LEVEL: info
           RENOVATE_REPOSITORIES: ${{ github.repository }}