doc: add release note entry about buildPython*.stdenv

nixos/doc/manual/release-notes/rl-2405.section.md

@@ -42,6 +42,19 @@ The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been m
   The `nimPackages` and `nim2Packages` sets have been removed.
   See https://nixos.org/manual/nixpkgs/unstable#nim for more information.
 
+- `buildPythonPackage.override` and `buildPythonApplication.override` is now available.
+
+- One can now specify custom `stdenv` with `buildPython*.override` when building Python packages. For example:
+
+  ```nix
+  buildPythonPackage.override { stdenv = ...; } {
+    pname = ...;
+    version = ...;
+  }
+  ```
+
+  This is now recommended over passing `stdenv` as a `buildPython*` argument.
+
 - The Yama LSM is now enabled by default in the kernel, which prevents ptracing
   non-child processes. This means you will not be able to attach gdb to an
   existing process, but will need to start that process from gdb (so it is a