feat: add git to required packages

[imlonghao]

The action docker/build-push-action build Docker images with buildx.

The docker-build is something like remote-build, it runs the build process on the remote host.
In this case, we need git in the Docker-In-Docker container image.

Close #57

[sebthom]

Could we make this conditional? That it is only installed for the dind image?

[imlonghao]

I moved the git installation under $FLAVOR == dind*, only dind image need git.

[sebthom]

Thanks!