add release note

Author: a-tarasyuk

clang/docs/ReleaseNotes.rst

@@ -714,6 +714,8 @@ Bug Fixes to C++ Support
   assumption if they also occur inside of a dependent lambda. (#GH114787)
 - Clang now uses valid deduced type locations when diagnosing functions with trailing return type
   missing placeholder return type. (#GH78694)
+- Clang now uses the location of the begin of the member expression for ``CallExpr``
+  involving deduced ``this``. (#GH116928)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^