ci: use GITHUB_TOKEN for authenticating against ghcr.io

Signed-off-by: Matthew Penner <me@matthewp.io>

Author: matthewpi

.github/workflows/docker.yaml

@@ -49,7 +49,7 @@ jobs:
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}
-          password: ${{ secrets.REGISTRY_TOKEN }}
+          password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Update version
         if: "github.event_name == 'release' && github.event.action == 'published'"