Add CHANGELOG entry for azure-cosmos 4.80.0 bump

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: tvaron3

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## Release History
 
+### 1.20.0 (Unreleased)
+#### Other Changes
+* Updated `azure-cosmos` version to `4.80.0`.
+
 ### 1.19.0 (2026-01-27)
 #### Key Bug Fixes
 * Updated `azure-cosmos` version to `4.77.0` to address these security vulnerabilities. - [PR 585](https://github.com/microsoft/kafka-connect-cosmosdb/pull/585)