minor #21233 Add Christopher Hertel as a core team member (welcoMattic)

This PR was submitted for the 7.4 branch but it was merged into the 6.4 branch instead.

Discussion
----------

Add Christopher Hertel as a core team member

Related to the announcement of Symfony AI
https://symfony.com/blog/kicking-off-the-symfony-ai-initiative
`@chr`-hertel 👏

Commits
-------

0576081 Add Christopher Hertel as a core team member

Author: OskarStark

contributing/core_team.rst

@@ -101,7 +101,8 @@ Active Core Members
   * **Berislav Balogović** (`hypemc`_);
   * **Mathias Arlaud** (`mtarld`_);
   * **Florent Morselli** (`spomky`_);
-  * **Alexandre Daubois** (`alexandre-daubois`_).
+  * **Alexandre Daubois** (`alexandre-daubois`_);
+  * **Christopher Hertel** (`chr-hertel`_).
 
 * **Security Team** (``@symfony/security`` on GitHub):
 
@@ -378,4 +379,5 @@ discretion of the **Project Leader**.
 .. _`spomky`: https://github.com/spomky/
 .. _`alexandre-daubois`: https://github.com/alexandre-daubois/
 .. _`tucksaun`: https://github.com/tucksaun/
+.. _`chr-hertel`: https://github.com/chr-hertel/
 .. _`the releases page`: https://symfony.com/releases