Help: Add 3.30 release notes for project variable updates

Add a 3.30.3 release note for commit c1ece78d11 (project: non cache
<project> prefix variables are also created, 2024-08-27, v3.30.3~2^2).
Prepare a 3.30.4 release note for commit 86ad7cc886 (project: Only
define non-cache vars if already defined, 2024-09-15).