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reference, has been replaced by using one of the following functions, which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_print.py

@@ -129,6 +129,17 @@ class TestPrint(unittest.TestCase):
                 raise RuntimeError
         self.assertRaises(RuntimeError, print, 1, file=noflush(), flush=True)
 
+    def test_gh130163(self):
+        class X:
+            def __str__(self):
+                sys.stdout = StringIO()
+                support.gc_collect()
+                return 'foo'
+
+        with support.swap_attr(sys, 'stdout', None):
+            sys.stdout = StringIO()  # the only reference
+            print(X())  # should not crash
+
 
 class TestPy2MigrationHint(unittest.TestCase):
     """Test that correct hint is produced analogous to Python3 syntax,