Heredocs in Dockerfiles dont work and show up as blank inside container when building images

building images with the docker SDK for python using Dockerfile's with heredocs show up as blank inside container.
Python code to reproduce

import docker
import os
import json

def build_docker_image():
    client = docker.from_env()
    # print(json.dumps(client.version(), indent=4))
    # print(json.dumps(client.info(), indent=4))
    image, _ = client.images.build(path='/Users/wick/DockerTest', platform="linux/amd64",, tag='rocky8-test:latest')
    print(f"Image {image.tags[0]} built successfully!")
    for log in _:
        print(log)

if __name__ == '__main__':
    build_docker_image()

Dockerfile used:

FROM rockylinux:8

RUN cat <<EOF > /tmp/test_file
test content
test content
test content
EOF

Results:
/tmp/test_file will be blank.

Additional info:
client.version() output:

{
    "Platform": {
        "Name": "Docker Desktop 4.28.0 (139021)"
    },
    "Components": [
        {
            "Name": "Engine",
            "Version": "25.0.3",
            "Details": {
                "ApiVersion": "1.44",
                "Arch": "amd64",
                "BuildTime": "2024-02-06T21:14:25.000000000+00:00",
                "Experimental": "false",
                "GitCommit": "f417435",
                "GoVersion": "go1.21.6",
                "KernelVersion": "6.6.16-linuxkit",
                "MinAPIVersion": "1.24",
                "Os": "linux"
            }
        },
        {
            "Name": "containerd",
            "Version": "1.6.28",
            "Details": {
                "GitCommit": "ae07eda36dd25f8a1b98dfbf587313b99c0190bb"
            }
        },
        {
            "Name": "runc",
            "Version": "1.1.12",
            "Details": {
                "GitCommit": "v1.1.12-0-g51d5e94"
            }
        },
        {
            "Name": "docker-init",
            "Version": "0.19.0",
            "Details": {
                "GitCommit": "de40ad0"
            }
        }
    ],
    "Version": "25.0.3",
    "ApiVersion": "1.44",
    "MinAPIVersion": "1.24",
    "GitCommit": "f417435",
    "GoVersion": "go1.21.6",
    "Os": "linux",
    "Arch": "amd64",
    "KernelVersion": "6.6.16-linuxkit",
    "BuildTime": "2024-02-06T21:14:25.000000000+00:00"
}

Start with the Python reproduction using client.images.build and the provided Dockerfile, then inspect how Dockerfile build input is prepared for the Docker Engine API. Verify the built image's /tmp/test_file contents; done means the heredoc content is preserved instead of appearing blank.