Request: Use `errors.As` instead of type assertions internally

[ian-oneleet]

I are trying to make this library play nicely with a custom http.Client that converts certain error responses to errors at a lower level. This (rightly) breaks some things, because the error type this Client returns isn't an error type that go-github recognizes. One way to solve this would be to errors.Join the custom error type with an *ErrorResponse instance, so that it acts as both error types.

The problem I've faced is that go-github sometimes type-asserts errors down to *ErrorResponse, instead of using errors.As:

• go-github/github/github.go

  Line 1184 in f137c94

  v, ok := target.(*ErrorResponse)

• go-github/github/github.go

  Line 1489 in f137c94

  if err, ok := err.(*ErrorResponse); ok && err.Response.StatusCode == http.StatusNotFound {

• go-github/github/repos.go

  Line 2370 in f137c94

  errorResponse, ok := err.(*ErrorResponse)

This is not a bug in the library, because our http.Client implementation technically breaks the API contract of http.Client; the doc comment above RoundTripper.RoundTrip says:

	// RoundTrip should not attempt to interpret the response. In
	// particular, RoundTrip must return err == nil if it obtained
	// a response, regardless of the response's HTTP status code.

This pattern of customizing errors at the http.Client level is nonetheless useful to us, and it would be helpful if go-github played nicely with it. I believe the only changes required would be to use errors.As instead of a direct type assertion at the three locations I mentioned above. Would you be accepting of such a change?

Thanks for your time.

[gmlewis]

If I recall correctly, there was a discussion about using errors.As and we held off on using it at the time due to the requirement that we support the two most recent versions of the Go compiler.

However, we are now well past that point and would be happy to accept PRs that use it as long as it doesn't introduce breaking changes to this client library.

[gmlewis]

Closed by #3739.