C++: Add changenote for changes to some queries

Queries affected:
    cpp/wrong-type-format-argument
    cpp/comparison-with-wider-type
    cpp/integer-multiplication-cast-to-long
    cpp/implicit-function-declaration
    cpp/suspicious-add-sizeof

Author: igfoo

cpp/ql/src/change-notes/2025-09-11-queries-demoted.md

@@ -0,0 +1,5 @@
+---
+category: majorAnalysis
+---
+* The queries `cpp/wrong-type-format-argument`, `cpp/comparison-with-wider-type`, `cpp/integer-multiplication-cast-to-long`, `cpp/implicit-function-declaration` and `cpp/suspicious-add-sizeof` have had their precisions reduced from `high` to `medium`. They will also now give alerts for projects built with `build-mode: none`.
+* The queries `cpp/wrong-type-format-argument`, `cpp/comparison-with-wider-type`, `cpp/integer-multiplication-cast-to-long` and `cpp/suspicious-add-sizeof` are no longer included in the `code-scanning` suite.