How to force-update the container image of a Container Action?

I went through the following steps to create a container action:

It uses this code to create the image:

runs:
  using: 'docker'
  image: 'Dockerfile'
  args:
    - ${{ inputs.who-to-greet }}

After 1st run, the workflow creates an image, and then the workflow uses the same image created, so the workflow runs much quicker.

The problem is that when I change the files inside the container (for example entrypoint.sh in the example link above), the container image is not being updated. It keeps using the older version of the file inside the outdated image.

How to force-update the container image of a Container Action?