Add min version for custom request support (#1668)

* Add min version for custom request support

* Use pytest <9.0.0

Author: ramya-stripe

README.md

@@ -275,6 +275,8 @@ Stripe has features in the [private preview phase](https://docs.stripe.com/relea
 
 ### Custom requests
 
+> This feature is only available from version 11 of this SDK.
+
 If you would like to send a request to an undocumented API (for example you are in a private beta), or if you prefer to bypass the method definitions in the library and specify your request details directly, you can use the `raw_request` method on `StripeClient`.
 
 ```python

deps/test-requirements.txt

@@ -14,4 +14,4 @@ anyio[trio] == 4.11.0; python_version >= "3.13"
 pytest-mock >= 2.0.0
 mock >= 4.0; python_version < "3.8"
 pytest-xdist >= 1.31.0
-pytest >= 6.0.0
+pytest >= 6.0.0,<9.0.0