ci: use new org-level dockerhub token (#126)

* Use new org-level dockerhub token

* Use vars, not secrets

Author: matthewelwell

.github/workflows/docker-publish-image.yml

@@ -38,8 +38,8 @@ jobs:
             - name: Login to DockerHub
               uses: docker/login-action@v3
               with:
-                  username: ${{ secrets.DOCKERHUB_USERNAME }}
-                  password: ${{ secrets.DOCKERHUB_TOKEN }}
+                  username: ${{ vars.DOCKERHUB_USERNAME_WRITE }}
+                  password: ${{ secrets.DOCKERHUB_TOKEN_WRITE }}
 
             - name: Build and push
               id: docker_build