Update HISTORY.md to describe version 8.0.0

Author: russella-acm

HISTORY.md

@@ -1,6 +1,6 @@
 # createsend-python history
 
-# v8.0.0 - 4 Dec, 2024
+## v8.0.0 - 4 Dec, 2024
 * Upgrades to allow this wrapper to be used with Python 3.12 and beyond.
 * Breaking: Python versions 3.5 and prior will no longer work with this version of the wrapper.