Mark fetchTree as stable

doc/manual/src/release-notes/rl-next.md

@@ -6,4 +6,6 @@
 
 - The experimental feature `repl-flake` is no longer needed, as its functionality is now part of the `flakes` experimental feature. To get the previous behavior, use the `--file/--expr` flags accordingly.
 
-- Introduce new flake installable syntax `flakeref#.attrPath` where the "." prefix denotes no searching of default attribute prefixes like `packages.<SYSTEM>` or `legacyPackages.<SYSTEM>`.
+- Introduce new flake installable syntax `flakeref#.attrPath` where the "." prefix denotes no searching of default attribute prefixes like `packages.<SYSTEM>` or `legacyPackages.<SYSTEM>`.
+
+- `builtins.fetchTree` is now marked as stable.

src/libexpr/primops/fetchTree.cc

@@ -213,7 +213,6 @@ static RegisterPrimOp primop_fetchTree({
           ```
     )",
     .fun = prim_fetchTree,
-    .experimentalFeature = Xp::Flakes,
 });
 
 static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v,