gh-154441: Skip the scheduler tests if the API requires privileges (GH-154442)

DragonFly BSD requires privileges to use the scheduler API, even for
the calling process.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_os/test_posix.py

@@ -46,7 +46,8 @@ def _supports_sched():
     try:
         posix.sched_getscheduler(0)
     except OSError as e:
-        if e.errno == errno.ENOSYS:
+        # DragonFly BSD requires privileges to use the scheduler API.
+        if e.errno in (errno.ENOSYS, errno.EPERM):
             return False
     return True
 
@@ -1453,6 +1454,7 @@ def test_bug_140634(self):
         del sched_priority, param  # should not crash
         support.gc_collect()  # just to be sure
 
+    @requires_sched
     @unittest.skipUnless(hasattr(posix, "sched_rr_get_interval"), "no function")
     def test_sched_rr_get_interval(self):
         try: