Switch changelog back to dev mode

Signed-off-by: Nathan Rebours <nathan.p.rebours@gmail.com>

Author: NathanReb

CHANGES.md

@@ -1,15 +1,11 @@
+unreleased
+----------
+
 0.34.0 (2025-01-06)
 -------------------
 
 ### 5.3 support
 
-5.3 support is being added gradually over the course of its development.
-This section should be updated with each relevant PR.
-
-Note to maintainers: until 5.3 support is officially released, this section
-should be excluded from the release, see [RELEASING.md](RELEASING.md) for
-details.
-
 - Add initial OCaml 5.3 support (#487, @NathanReb, @hhugo, @nojb)
 
 - Initialise OCaml 5.3's lexer with the `keywords` setting from `OCAMLPARAM` or