C++: Update change note.

Author: geoffw0

cpp/ql/src/change-notes/2026-03-23-implicit-function-declaration.md

@@ -1,4 +1,5 @@
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 category: minorAnalysis
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+* The "Implicit function declaration" (`cpp/implicit-function-declaration`) query has been promoted to `@precision high`.
 * The "Implicit function declaration" (`cpp/implicit-function-declaration`) query no longer produces results on `build mode: none` databases. These results were found to be very noisy and fundamentally imprecise in this mode.