Unpinned from 8.4.0

Due to bug in type annotations
https://bugs.mysql.com/bug.php?id=117347

Author: FreddieAkeroyd

installation_and_upgrade/requirements.txt

@@ -12,4 +12,4 @@ pyepics
 epicscorelibs
 certifi  # Needed in order for requests to find https certificates
 requests
-mysql-connector-python==8.4.0
+mysql-connector-python