minor #14585 [Messenger] Add mention about serialize in inMemory transport dsn (tyx)

This PR was merged into the 5.3-dev branch.

Discussion
----------

[Messenger] Add mention about serialize in inMemory transport dsn

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/releases for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `5.x` for features of unreleased versions).

-->

fix #14584

Commits
-------

26dfa83 [Messenger] Add mention about serialize in inMemory transport dsn

Author: javiereguiluz

messenger.rst

@@ -1316,6 +1316,15 @@ during a request::
         :class:`Symfony\\Bundle\\FrameworkBundle\\Test\\KernelTestCase`
         or :class:`Symfony\\Bundle\\FrameworkBundle\\Test\\WebTestCase`.
 
+.. tip::
+
+    Using ``in-memory://?serialize=true`` as dsn will perform message serialization as real asynchronous transport will do.
+    Useful to test an additional layer, especially when you use your own message serializer.
+
+.. versionadded:: 5.3
+
+    The ``in-memory://?serialize=true`` dsn was introduced in Symfony 5.3.
+
 Amazon SQS
 ~~~~~~~~~~