docs: add buildDotnetModule changes to release notes.

nixos/doc/manual/release-notes/rl-2411.section.md

@@ -911,6 +911,12 @@
 
 - `virtualisation.incus` module gained new `incus-user.service` and `incus-user.socket` systemd units. It is now possible to add a user to `incus` group instead of `incus-admin` for increased security.
 
+- `buildDotnetModule` now uses JSON-based instead of nix-based lockfiles.
+  Support for nix-based lockfiles has been deprecated and will be dropped on release 25.11.
+
+- `buildDotnetModule.fetch-deps` now generates a JSON lockfile by default.
+  A nix-based lockfile will be generated if one existed before for compatibility, however it has been deprecated and will be dropped on release 25.11.
+
 - `freecad` now supports addons and custom configuration in nix-way, which can be used by calling `freecad.customize`.
 
 - `buildNimSbom` was added as an alternative to `buildNimPackage`. `buildNimSbom` uses [SBOMs](https://cyclonedx.org/) to generate packages whereas `buildNimPackage` uses a custom JSON lockfile format.