Update changelog

Author: baptiste0928

CHANGELOG.md

@@ -13,6 +13,9 @@ however, insignificant breaking changes do not guarantee a major version bump, s
 - Loading the blocked list with the `?blocked` command takes a long time when the list is large. ([PR #3242](https://github.com/kyb3r/modmail/pull/3242))
 - Reply not being forwarded from DM. (PR [#3239](https://github.com/modmail-dev/modmail/pull/3239))
 
+### Changed
+- Guild icons in embed footers and author urls now have a fixed size of 128. ([PR #3261](https://github.com/modmail-dev/modmail/pull/3261))
+
 # v4.0.2
 
 ### Breaking