Increase reliablity of Go container builds for less common platforms

[jauderho]

This seems to be a more common issue now so bringing it up for input/discussion.

Go container builds seem to fail frequently due to net/http: TLS handshake timeout issues on ppc64le, s390x etc. platforms. The failure seems to be arbitrary as I am usually able to reach the timed out file via curl/browser without issue. The frustrating part is this only seems to happen on the less commonly used platforms.

Here is one of the failed runs: https://github.com/jauderho/dockerfiles/runs/3932654484?check_suite_focus=true#step:8:1456

Part of the original impetus of building images was the fact that most official builds appeared to lack builds other than amd64 & arm64. So I can either stop attempting ppc64le builds until the goproxy infrastructure improves or risk having to babysit failing builds until they sort themselves out.

See also https://github.com/moby/buildkit/issues/2402

[jauderho]

For now, ppc64le builds are pretty much disabled across the board as they were generating too many failed runs.

[jauderho]

Re-added ppc64le builds. Seems sorted now...