Fix issue 11493 - Correctly explain code snippet behaviour

[matthriscu]

Signed-off-by: Matei Hriscu matei.hriscu@proton.me

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	11493	normal	dlang.org/type.html incorrectly says that you can't cast from -1 to unsigned types