Add a release note entry

Author: ahatanak

clang/docs/ReleaseNotes.rst

@@ -437,6 +437,8 @@ Bug Fixes to C++ Support
 - Fix the result of `__builtin_is_implicit_lifetime` for types with a user-provided constructor. (#GH160610)
 - Correctly deduce return types in ``decltype`` expressions. (#GH160497) (#GH56652) (#GH116319) (#GH161196)
 - Fixed a crash in the pre-C++23 warning for attributes before a lambda declarator (#GH161070).
+- Fixed a crash that occurred when a static constexpr data member of a class
+  template was declared with an incomplete type. (#GH120371)
 
 Bug Fixes to AST Handling
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