[3.12] Add tests for failing PyUnicode_AsUTF8AndSize() with psize=NULL (GH-111100) (GH-111105)

(cherry picked from commit b60f058)

Co-authored-by: Serhiy Storchaka <[email protected]>

Author: miss-islington

Lib/test/test_capi/test_unicode.py

@@ -902,7 +902,11 @@ def test_asutf8andsize(self):
         self.assertRaises(UnicodeEncodeError, unicode_asutf8andsize, '\ud8ff', 0)
         self.assertRaises(TypeError, unicode_asutf8andsize, b'abc', 0)
         self.assertRaises(TypeError, unicode_asutf8andsize, [], 0)
+        self.assertRaises(UnicodeEncodeError, unicode_asutf8andsize_null, '\ud8ff', 0)
+        self.assertRaises(TypeError, unicode_asutf8andsize_null, b'abc', 0)
+        self.assertRaises(TypeError, unicode_asutf8andsize_null, [], 0)
         # CRASHES unicode_asutf8andsize(NULL, 0)
+        # CRASHES unicode_asutf8andsize_null(NULL, 0)
 
     @support.cpython_only
     @unittest.skipIf(_testcapi is None, 'need _testcapi module')