chore: Add external contributor to CHANGELOG.md (#18952)

This PR adds the external contributor to the CHANGELOG.md file, so that
they are credited for their contribution. See #18900

Co-authored-by: JPeer264 <10677263+JPeer264@users.noreply.github.com>

Author: javascript-sdk-gitflow[bot]

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 - "You miss 100 percent of the chances you don't take. — Wayne Gretzky" — Michael Scott
 
+Work in this release was contributed by @sebws. Thank you for your contribution!
+
 - **feat(tanstackstart-react): Auto-instrument global middleware in `sentryTanstackStart` Vite plugin ([#18884](https://github.com/getsentry/sentry-javascript/pull/18844))**
 
   The `sentryTanstackStart` Vite plugin now automatically instruments `requestMiddleware` and `functionMiddleware` arrays in `createStart()`. This captures performance data without requiring manual wrapping.