Missing `Errors() []error` if used Go 1.20

[prochac]

Ok, my bad, now it's Unwrap() []error.
IMO it should be noted somewhere, that the behavior of the library varies based on the version of used Go.
It can cause backward incompatibility to some.

Old text:
The errors.Join() feature in Go 1.20 is nice, but it's not possible to split the errors back to slice of errors.

With Uber implementation, that's under build tag for Go 1.19, it is possible

[jdorfman]

@camdencheek thoughts?

[camdencheek]

The goal of using the uber implementation for go 1.19 was to keep errors.Is and errors.As working as expected. I don't think it's possible to make the transition completely backwards compatible, but I'll add a note to the docs.

Thanks for the callout!