gh-130163: Fix crashes related to PySys_GetObject() (GH-130503)

The use of PySys_GetObject() and _PySys_GetAttr(), which return a borrowed
reference, has been replaced by using one of the following functions, which
return a strong reference and distinguish a missing attribute from an error:
_PySys_GetOptionalAttr(), _PySys_GetOptionalAttrString(),
_PySys_GetRequiredAttr(), and _PySys_GetRequiredAttrString().

Lib/test/test_sys.py

@@ -2,6 +2,7 @@ import builtins
 import codecs
 import _datetime
 import gc
+import io
 import locale
 import operator
 import os
@@ -80,6 +81,18 @@ class DisplayHookTest(unittest.TestCase):
             code = compile("42", "<string>", "single")
             self.assertRaises(ValueError, eval, code)
 
+    def test_gh130163(self):
+        class X:
+            def __repr__(self):
+                sys.stdout = io.StringIO()
+                support.gc_collect()
+                return 'foo'
+
+        with support.swap_attr(sys, 'stdout', None):
+            sys.stdout = io.StringIO()  # the only reference
+            sys.displayhook(X())  # should not crash
+
+
 class ActiveExceptionTests(unittest.TestCase):
     def test_exc_info_no_exception(self):
         self.assertEqual(sys.exc_info(), (None, None, None))