Update CHANGELOG

Author: Aberdur

CHANGELOG.md

@@ -38,6 +38,7 @@ Code contributions to the release:
 - Add create_summary_tables.py to assets to process data from a given epidemiological week [#418](https://github.com/BU-ISCIII/relecov-tools/pull/418)
 - Add wrapper to github actions (test_sftp_modules) [#409](https://github.com/BU-ISCIII/relecov-tools/pull/409)
 - Remove wrapper from github actions (test_sftp_modules) [#421](https://github.com/BU-ISCIII/relecov-tools/pull/421)
+- Add Validation for Dropdown Columns: Notify Users of Invalid Entries in build-schema module [#423](https://github.com/BU-ISCIII/relecov-tools/pull/423)
 
 #### Fixes