The Method I Used Until Now

Dockerfile

# syntax=docker/dockerfile:1.0.0-experimental
FROM python:3.10-bullseye

RUN mkdir -p -m 0600 ~/.ssh && ssh-keyscan github.com >> ~/.ssh/known_hosts
RUN --mount=type=ssh ssh git@github.com

sh

DOCKER_BUILDKIT=1 docker build . --platform linux/amd64 --ssh default -t test-build -f Dockerfile

This Works Well

Dockerfile

FROM python:3.10-bullseye

RUN --mount=type=ssh ssh -o StrictHostKeyChecking=no git@github.com

sh

docker build . --platform linux/amd64 --ssh default -t test-build -f Dockerfile

However, if you are installing from a private git repository using pip install, you should include this:

RUN mkdir -p -m 0600 ~/.ssh && ssh-keyscan github.com >> ~/.ssh/known_hosts