pthread_create error with GitHub Actions

[QartemisT]

With the latest release of lanes, there's exceptions being thrown by lanes;

src/threading.c 842: pthread_create() failed, 1 EPERM

This was not occuring before this last release.

It appears that this commit broke this; https://github.com/LuaLanes/lanes/commit/d73f4cee37b0a43edadf9709289798ee4bfccc0e

[Mitalie]

Not specific to GitHub Actions, but happens generally on Linux when built without -DLINUX_SCHED_RR and run as non-root:

• The first time the table returned from require "lanes" is accessed, lanesMeta.__index calls lanes.configure which calls gen( "*", { package= {}, priority = max_prio}, timer_body)() in the first_time block.
• max_prio comes from THREAD_PRIO_MAXon the C side, defined as (sudo ? +3 : 0) so 0 for non-root.
• Before d73f4ce, prio == 0 was treated as no-op in THREAD_CREATE. Now, it's different from THREAD_PRIO_DEFAULT and root permission is not confirmed when built without -DLINUX_SCHED_RR. THREAD_CREATE attempts to create a thread with policy SCHED_RR, priority 50, which fails for non-root.