CI | remove duplicated image building for PR CI?

[Xynnn007]

Now when we make a PR, there will be bunch of image building tests. Most of them are for different archs.

we nearly never met "failure only happens on one arch" case.

Thus a suggestion would be to simplify the "PR" test matrix, that is to only test building on x86-64. At the same time, we keep full matrix for "push" to build and release.

[fitzthum]

I am fine with building on all the arches for the PRs. Has this been a bottleneck?

[Xynnn007]

It is for the sake of optimization and saving resources. Basically the idea is that "if no use, we do not need to do".
But "if no use" is my idea, I'd like to get more opinions about whether it's useful.

[mythi]

The fact that something hasn't happened in the past does not mean it could not happen. I at least trust PR checks a lot so reducing coverage does not sound like a useful optimization.

What we could potentially do (based on checking what is build in #1530) is to see how Build Staged Images and Build e2e materials could share content.

The other matrix dimension could also be checked for improvements. For example, the ITA flavor could be merged in other images because the AS selection is not mutually exclusive.