docs(changelog): changelog for lts-v2.8.31 release

Change-Id: I030ee0b33663a7b35b2efeeee295b700dbf3541e
Signed-off-by: Release CI <ci@trustedfirmware.org>
diff --git a/docs/conf.py b/docs/conf.py
index b39659c..1d89195 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -14,8 +14,8 @@
 
 project = "Trusted Firmware-A"
 author = "Trusted Firmware-A contributors"
-version = "2.8.30"
-release = "2.8.30"
+version = "2.8.31"
+release = "2.8.31"
 
 # -- General configuration ---------------------------------------------------