Used QEMU to move Travis CI jobs to GHA

[radarhere]

Despite previous evidence that our TravisCI credits were not running out, there is now a message at https://app.travis-ci.com/github/python-pillow/pillow-wheels

So this PR is reviving #247, in case we would like to move the aarch64 jobs to GitHub Actions using QEMU.

[hugovk]

Thanks for reviving this!

Hopefully we can get Travis back (will continue in the main issue), these are very slow to build.

I spotted there's a newish thing on GitHub Actions. From the build summary page it shows the total duration: 6h 47m 9s. For comparison, the last main build was 2h 24m 35s. This is the wall clock time.

The total duration is a link, click it and you can see the times per job.

With main, each ranged from around 8m to 30m, all totalling 16h 24m 55s.

With this PR, we get new ones from around 1h 37m to 4h 3m! All totalling 4d 4h 1m 38s!

(We are building twice here, -latest and regular, that may be something to reconsider.)

[radarhere]

Closing, now that python-pillow/Pillow#7418 has moved the code into the main repository.