How to read docker-compose secrets file as environment variables from unadapted image

docker-compose.yml

version: "3.9"
services:
  read_secret_simple:
    build: .
    secrets:
      - my_secret

  read_secret_existing_image:
    image: registry
    entrypoint: [ "sh", "/run/secrets/my_secret2" ]
    secrets:
      - my_secret2

secrets:
  my_secret:
    file: ./my_secret.sh
  my_secret2:
    file: ./my_secret2.sh

Dockerfile

FROM busybox

CMD [ "sh", "/run/secrets/my_secret" ]

my_secret.sh

#!/bin/bash

export MY_SECRET=GERBILS

printenv

# use normal entrypoint from default docker
date

my_secret2.sh

#!/bin/bash

export MY_SECRET=GERBILS
export REGISTRY_HTTP_SECRET=2GERBILS

printenv

# use normal entrypoint from default docker
/entrypoint.sh /etc/docker/registry/config.yml