Update CHANGELOG

For eng/ide/ada_language_server#1576

Author: AnthonyLeonardoGracio

CHANGELOG.md

@@ -6,6 +6,7 @@ section below it for the last release. -->
 
 * Support single-line (`//`) and multi-line (`/* */`) comments in ALS JSON configuration files
 * Fix the reporting of test results in the Testing view when the test tree is not expanded
+* Fix sluggish completion in GPR files after editing them
 
 ## 26.0.202412190