[errors] Build should return an error

[EtienneM]

The Build method on ValidationErrorsBuilder should return a pure error rather than a *errors.ValidationErrors:

go-utils/errors/validation_errors.go

Line 88 in 8aba6f4

func (v *ValidationErrorsBuilder) Build() *ValidationErrors {

The current situation may lead to a staticcheck offense never returns a nil interface value. The root cause of this issue is explained here (https://go.dev/doc/faq#nil_error):

It's a good idea for functions that return errors always to use the error type in their signature (as we did above) rather than a concrete type such as *MyError, to help guarantee the error is created correctly

Initially discussed here: https://scalingo.slack.com/archives/C01E42AT2G6/p1717062547454579