CHANGES.md: document BLAKE2b's "size"-setting support

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from #22583)

CHANGES.md

@@ -33,6 +33,11 @@ OpenSSL 3.2
 
 ### Changes between 3.1 and 3.2 [xx XXX xxxx]
 
+ * The BLAKE2b hash algorithm supports a configurable output length
+   by setting the "size" parameter.
+
+   *Čestmír Kalina and Tomáš Mráz*
+
  * Enable extra Arm64 optimization on Windows for GHASH, RAND and AES.
 
    *Evgeny Karpov*