Fix release notes

Author: dstansby

docs/release.rst

@@ -18,20 +18,28 @@ Release notes
    See `GH1777 <https://github.com/zarr-developers/zarr-python/issues/1777>`_ for more details on the upcoming
    3.0 release.
 
-.. _release_2.18.2:
-
-Enhancements
-~~~~~~~~~~~~
 
-* Add Zstd codec to old V3 code path.
-  By :user:`Ryan Abernathey <rabernat>`
+Unreleased
+----------
 
 Maintenance
 ~~~~~~~~~~~
 
 * Removed support for Python 3.9.
   By :user:`David Stansby <dstansby>`
 
+
+.. _release_2.18.2:
+
+2.18.2
+------
+
+Enhancements
+~~~~~~~~~~~~
+
+* Add Zstd codec to old V3 code path.
+  By :user:`Ryan Abernathey <rabernat>
+
 .. _release_2.18.1:
 
 2.18.1