Bunch slower aarch64 jobs first to speed up build

[hugovk]

Updates python-pillow#247.

By moving the platform: matrix factor first we can get the bottleneck aarch64 jobs queued up sooner and so let them (and therefore the whole build) finish sooner.

On my fork, this took 2h 21m 57s:

• https://github.com/hugovk/pillow-wheels/actions/runs/1785155556

The baseline took 2h 51m 43s:

• https://github.com/radarhere/pillow-wheels/actions/runs/1763682103

(Still not convinced whether to ditch faster Travis for this just yet.)

[radarhere]

Nice.
Sure, feel free to not be convinced. Even if this doesn't make it in, it's still good to know how to migrate to GHA, and what happens if we do.
I had also expected this to be useful if Travis ever took an unfortunate amount of time to renew our credits - I did not expect your news that our credits are not actually decreasing.

[hugovk]

Yes, I was surprised to see the credits staying the same. I'm not surprised by the lack of communication from new Travis CI about what's really going on, and won't be surprised if it just stops working with no notice, so it's great we have this as a backup! 👍