ref: Add external contributor to CHANGELOG.md (getsentry#13535)

This PR adds the external contributor to the CHANGELOG.md file, so that
they are credited for their contribution. See getsentry#13524

Co-authored-by: lforst <[email protected]>

Author: github-actions[bot]

Diff for: 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 @leopoldkristjansson. Thank you for your contribution!
+
 ### Important Changes
 
 - **fix(browser): Remove faulty LCP, FCP and FP normalization logic (#13502)**