Use larger GitHub runners for build actions

[mgeisler]

We apparently have access to larger runners on the GitHub Enterprise plan.

[mgeisler]

The standard GitHub-hosted runners have 4 cores for Linux.

Using the 64-core runner removes ~1 minute for the per-language builds. Compare

• Before, #1963
• After, #1964

So the time per language shrinks from about 4.5 minutes to 3.5 minutes. This is not super impressive and I guess this is mainly because we have lots of serial work in our jobs: building the and testing the translation takes the same amount of time in both cases. It's basically only the cargo install steps that improve because of much better parallelism.

I'm now testing the publish workflow, but I expect similar results since this also mostly consist of single-threaded steps.

[mgeisler]

The two publish jobs:

• Before: 17m 16s in total, 23s used for uploading the page.
• After, this PR: 17m 6s in total, without uploading the page.

I think this means that it's not worth using the larger runners for us.

[mgeisler]

cc @qwandor, @djmitche, @randomPoison in case you had been wanting to experiment this this.