Use StatusCodes.Status404NotFound instead of 404 (#18453)
Use StatusCodes.Status404NotFound instead of 404 (#18453)

This is a minor change to improve consistency and use `StatusCodes` members instead of raw harcoded status code numbers. It may help beginners browsing through the code-base to find where the default 404 response comes from for unmatched requests.
aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore