add release note

Author: martindurant

docs/release-notes.rst

@@ -13,6 +13,8 @@ Bug fixes
 
 * Fixes a bug that prevented reading Zarr format 2 data with consolidated metadata written using ``zarr-python`` version 2 (:issue:`2694`).
 
+* Ensure that compressor=None results in no compression in v2 (:issue:`2708`)
+
 Behaviour changes
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