Fix cmp_null missing parens in the example

[profetia]

Closes #16281

changelog: [cmp_null] Don't suggest to inline macro contents instead of calling them

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[Jarcho]

Thank you.

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[Jarcho]

For future reference if you want to add multiple things to the changelog you need to prefix each line with changelog:. Also documentation changes don't need changelog notes.

Your phrasing for the macro fix also doesn't really make sense. Macros are never mangled so a suggestion can't unmangle them. The suggestion we generate is mangled because it inlines the macro contents. Alternative wordings could be "Don't mangle suggestions involving macro calls" or "Don't suggest to inline macro contents instead of calling them".