Keep this up to date in all non-security-only branches, because the node.js
runtime for older versions might get deprecated in the future and fixing this
for all branches at once is easier.
Some jobs on GA apparently consume a lot of CPU resources, possibly hindering
communication between master and runner. This only seems to happen on Linux+ASAN
and macOS. For these jobs, keep one core idle.
Closes GH-12742
Tim Düsterhus