Update Docker workflow to use secrets for Gitea credentials in login step

Signed-off-by: Stephen Simpson <ssimpson89@users.noreply.github.com>

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

@@ -26,8 +26,8 @@ jobs:
         uses: docker/login-action@v3
         with:
           registry: ${{ env.REGISTRY }}
-          username: ${{ gitea.actor }}
-          password: ${{ secrets.GITEA_TOKEN }}
+          username: ${{ secrets.USER }}
+          password: ${{ secrets.PASS }}
 
       - name: Extract metadata for Docker
         id: meta