gh-138163: scheduler tests for posix_spawn fail on glibc for SCHED_BATCH

Author: jxes993409

Lib/test/test_posix.py

@@ -2036,6 +2036,9 @@ def test_setscheduler_only_param(self):
     @requires_sched
     @unittest.skipIf(sys.platform.startswith(('freebsd', 'netbsd')),
                      "bpo-34685: test can fail on BSD")
+    @unittest.skipIf(platform.libc_ver()[0] == 'glibc' and
+                     os.sched_getscheduler(0) in [os.SCHED_BATCH, os.SCHED_IDLE, os.SCHED_DEADLINE],
+                     "On glibc, posix_spawnattr_setschedpolicy cannot change the policy")
     def test_setscheduler_with_policy(self):
         policy = os.sched_getscheduler(0)
         priority = os.sched_get_priority_min(policy)