Add test for extending native errors w/o altering prototype

[jonchurch]

This adds a test to assert on behavior outlined in the docs but not captured in the test suite.

https://github.com/jshttp/http-errors?tab=readme-ov-file#createerrorstatus-error-properties

createError([status], [error], [properties])

Extend the given error object with createError.HttpError
properties. This will not alter the inheritance of the given
error object, and the modified error object is the
return value.

[carpasse]

This change looks good to me.
@jonchurch CI should stop failing if you rebase your branch against master.