Document that `test.support.bytecode_helper` is new in 3.9 (GH-22618) (GH-22761)

(cherry picked from commit cf693e537dc8aaa14315a7f59baec4a31d1167d3)

Co-authored-by: Saiyang Gou <gousaiyang@163.com>

Co-authored-by: Saiyang Gou <gousaiyang@163.com>
diff --git a/Doc/library/test.rst b/Doc/library/test.rst
index f7e6eba..e24f69c 100644
--- a/Doc/library/test.rst
+++ b/Doc/library/test.rst
@@ -1609,6 +1609,8 @@
 The :mod:`test.support.bytecode_helper` module provides support for testing
 and inspecting bytecode generation.
 
+.. versionadded:: 3.9
+
 The module defines the following class:
 
 .. class:: BytecodeTestCase(unittest.TestCase)