It'd be good if a job could be set up to completely block an entire category.
Use-case for this would be having a “writer” job that e.g. updates a server,
and having a set of “reader” jobs that contact that server. The “writer” job
would completely block the “use-server” category from running any
concurrent builds, and the “reader” jobs would just use 1 slot of the
allocated slots for that category.