Document bug fix in CHANGELOG

For eng/ide/ada_language_server#1610

Author: AnthonyLeonardoGracio

CHANGELOG.md

@@ -5,6 +5,8 @@ section below it for the last release. -->
 
 ## \<next>
 
+* Fix a bug that caused the ALS to hang when trying to complete partially qualified invisible symbols
+
 ## 26.0.202502240
 
 * Support single-line (`//`) and multi-line (`/* */`) comments in ALS JSON configuration files