Boinc does not use more than 1 core with a single project, revert to limiting to 1 core

3 jobs for master in 39 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #20374
test:build

00:00:16

passed #20375
test:json

00:00:16

 
  Push
passed #20376
push:hub

00:00:22