docs(changelog): changelog for lts-v2.8.20 release

Change-Id: I8e1567e4febc838d38da4abaf4ce24426ec921f8
Signed-off-by: Release CI <ci@trustedfirmware.org>
diff --git a/docs/conf.py b/docs/conf.py
index e78e6bc..3837ed5 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -14,8 +14,8 @@
 
 project = "Trusted Firmware-A"
 author = "Trusted Firmware-A contributors"
-version = "2.8.19"
-release = "2.8.19"
+version = "2.8.20"
+release = "2.8.20"
 
 # -- General configuration ---------------------------------------------------