doc: releases: 3.0: Update security notes

A CVE just left the embargo period before the release.

Signed-off-by: Flavio Ceolin <[email protected]>

Author: Flavio Ceolin

doc/releases/release-notes-3.0.rst

@@ -25,7 +25,8 @@ https://docs.zephyrproject.org/latest/security/vulnerabilities.html
 * CVE-2021-3861: `Zephyr project bug tracker GHSA-hvfp-w4h8-gxvj
   <https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-hvfp-w4h8-gxvj>`_
 
-* CVE-2021-3966: Under embargo until 2021-02-12
+* CVE-2021-3966: `Zephyr project bug tracker GHSA-hfxq-3w6x-fv2m
+  <https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-hfxq-3w6x-fv2m>`_
 
 Known issues
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