Changelog for deleting unsent reports in the background (#7346)

Author: samedson

Crashlytics/CHANGELOG.md

@@ -1,6 +1,7 @@
 # v7.5.0
 - [changed] Improve start-up performance by moving some initialization work to a background thread (#7332).
 - [changed] Updated upload-symbols to a version that is notarized to avoid macOS security alerts (#7323).
+- [changed] Deleting unsent reports with deleteUnsentReports no longer happens on the main thread (#7298).
 
 # v7.4.0
 - [changed] Removed obsolete crash reporting mechanism from the SDK (#7076).