Update CHANGELOG.md (#2059)

Author: HazAT

CHANGELOG.md

@@ -1,5 +1,14 @@
 # Changelog
 
+## 1.21.1
+
+### Various fixes & improvements
+
+- Do not send monitor_config when unset (#2058) by @evanpurkhiser
+- Add `db.system` span data (#2040, #2042) by @antonpirker
+- Fix memory leak in profiling (#2049) by @Zylphrex
+- Fix crash loop when returning none in before_send (#2045) by @sentrivana
+
 ## 1.21.0
 
 ### Various fixes & improvements