gh-117061: Fix test_posix.test_sched_setaffinity() on RHEL9 (#117126)

On RHEL9, sched_setaffinity(0, []) does not fail.

Author: vstinner

Lib/test/test_posix.py

@@ -1335,12 +1335,21 @@ def test_sched_getaffinity(self):
     def test_sched_setaffinity(self):
         mask = posix.sched_getaffinity(0)
         self.addCleanup(posix.sched_setaffinity, 0, list(mask))
+
         if len(mask) > 1:
             # Empty masks are forbidden
             mask.pop()
         posix.sched_setaffinity(0, mask)
         self.assertEqual(posix.sched_getaffinity(0), mask)
-        self.assertRaises(OSError, posix.sched_setaffinity, 0, [])
+
+        try:
+            posix.sched_setaffinity(0, [])
+            # gh-117061: On RHEL9, sched_setaffinity(0, []) does not fail
+        except OSError:
+            # sched_setaffinity() manual page documents EINVAL error
+            # when the mask is empty.
+            pass
+
         self.assertRaises(ValueError, posix.sched_setaffinity, 0, [-10])
         self.assertRaises(ValueError, posix.sched_setaffinity, 0, map(int, "0X"))
         self.assertRaises(OverflowError, posix.sched_setaffinity, 0, [1<<128])