Restore build processes for ESR 91

[llewelld]

I dropped the number of processes the build uses down to 1. See 629c8b36c58cc59a167a8290588995fef1242145.

This allows the build to progress without hanging locally. It might also do the same on OBS but I've not tested that.

Ideally we should figure out why higher process counts cause the build to hang, fix it, and up the process count again (i.e. revert this change).