[Docs] Add release note for #80963 fix

Author: Megan0704-1

clang/docs/ReleaseNotes.rst

@@ -293,6 +293,7 @@ Bug Fixes to Attribute Support
 Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
+- Clang now diagnoses copy constructors taking the class by value in template instantiations. (#GH130866)
 - Clang is now better at keeping track of friend function template instance contexts. (#GH55509)
 - Clang now prints the correct instantiation context for diagnostics suppressed
   by template argument deduction.