Update bytecode magic number for the 3.15 release candidate

Author: hugovk

Lib/test/test_importlib/test_util.py

@@ -647,7 +647,7 @@ def test_magic_number(self):
         # stakeholders such as OS package maintainers must be notified
         # in advance. Such exceptional releases will then require an
         # adjustment to this test case.
-        EXPECTED_MAGIC_NUMBER = 3625
+        EXPECTED_MAGIC_NUMBER = 3666
         actual = int.from_bytes(importlib.util.MAGIC_NUMBER[:2], 'little')
 
         msg = (