C++: Add change note

Author: jketema

cpp/ql/src/change-notes/2023-08-09-badly-bounded-write.md

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+---
+category: minorAnalysis
+---
+* The `cpp/badly-bounded-write` query could report false positives when a pointer was first initialized with a literal and later assigned a dynamically allocated array. These false positives now no longer occur.