In the build phase, an image is created. In the release phase, this image is deployed to Azure Container Instance (ACI) as container. Your error message suggests that in the build phase, no image is created. This takes place in step 30_createImageFromModel.py, where the IDs of the image is written to image.json. In 40_deployImageToACI.py, this json file is used to retrieve the image to deploy is.
Can you verify if you can find model “databricksmodel.mml” is part of your Azure ML Service workspace (script 20_buildModelDatabricks.py) and subsequently, if databricksmodel is part of your Azure Container Registry (30_createImageFromModel.py)?