[3.13] gh-102184: Test os.sync() only if the "walltime" resource is enabled (GH-155448) (GH-155463)

Calling sync() flushes all filesystem buffers and can block for a long
time, so it should not run in the default test suite.
(cherry picked from commit e45d456)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Alexey Izbyshev <izbyshev@ispras.ru>

Author: 3 people

Lib/test/test_posix.py

@@ -71,7 +71,7 @@ def testNoArgFunctions(self):
         NO_ARG_FUNCTIONS = [ "ctermid", "getcwd", "getcwdb", "uname",
                              "times", "getloadavg",
                              "getegid", "geteuid", "getgid", "getgroups",
-                             "getpid", "getpgrp", "getppid", "getuid", "sync",
+                             "getpid", "getpgrp", "getppid", "getuid",
                            ]
 
         for name in NO_ARG_FUNCTIONS:
@@ -81,6 +81,13 @@ def testNoArgFunctions(self):
                     posix_func()
                     self.assertRaises(TypeError, posix_func, 1)
 
+    # gh-102184: sync() can block for a long time.
+    @support.requires_resource('walltime')
+    @unittest.skipUnless(hasattr(posix, 'sync'), 'test needs posix.sync()')
+    def test_sync(self):
+        posix.sync()
+        self.assertRaises(TypeError, posix.sync, 1)
+
     @unittest.skipUnless(hasattr(posix, 'getresuid'),
                          'test needs posix.getresuid()')
     def test_getresuid(self):