ref: Add external contributor to CHANGELOG.md (#13298)

This PR adds the external contributor to the CHANGELOG.md file, so that
they are credited for their contribution. See #13296

---------

Co-authored-by: andreiborza <168741329+andreiborza@users.noreply.github.com>
Co-authored-by: Andrei Borza <andrei.borza@sentry.io>

CHANGELOG.md

@@ -10,6 +10,8 @@
 
 - "You miss 100 percent of the chances you don't take. — Wayne Gretzky" — Michael Scott
 
+Work in this release was contributed by @MonstraG. Thank you for your contribution!
+
 ## 8.25.0
 
 ### Important Changes