Specify Docker architecture explicitly in Makefile tasks (#1297)
Specify Docker architecture explicitly in Makefile tasks (#1297)

Currently when any of the Docker related `Makefile` targets are invoked
from a machine that is not using the AMD64 (x86-64) architecture (such
as a machine using the Apple M1), it emits the following warning:

```
WARNING: The requested image's platform (linux/amd64) does not match the
detected host platform (linux/arm64/v8) and no specific platform was requested
```

In addition, were the `heroku/heroku:*` images ever to support ARM64
(see https://github.com/heroku/stack-images/issues/194), relying on an
implicit platform value would mean the runtime generation tasks would
silently start to generate binaries for a different architecture.

To prevent this warning, and prevent such surprises with binary
generation, the platform is now specified explicitly using `--platform`.

GUS-W-10884947.
Scalingo/python-buildpack,heroku/heroku-buildpack-python,Scalingo/python-buildpack,heroku/heroku-buildpack-python