docs: add buildDotnetModule changes to release notes.

nixos/doc/manual/release-notes/rl-2505.section.md

@@ -146,6 +146,12 @@
 
 - `networking.wireguard` now has an optional networkd backend. It is enabled by default when `networking.useNetworkd` is enabled, and it can be enabled alongside scripted networking with `networking.wireguard.useNetworkd`. Some `networking.wireguard` options have slightly different behavior with the networkd and script-based backends, documented in each option.
 
+- `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.
+
 - `services.avahi.ipv6` now defaults to true.
 
 - `bind.cacheNetworks` now only controls access for recursive queries, where it previously controlled access for all queries.