Fix HTTP error handling in RESTClient.Request() method

- Ensure that `Request()` calls HandleHTTPError so that any JSON error body properly gets parsed;
- Ensure that response body is closed after reading the error response.

example_gh_test.go

@@ -77,10 +77,6 @@ func ExampleRESTClient_request() {
 	}
 	defer resp.Body.Close()
 
-	if resp.StatusCode > 299 {
-		log.Fatal("server error")
-	}
-
 	f, err := os.CreateTemp("", "*_checksums.txt")
 	if err != nil {
 		log.Fatal(err)

internal/api/rest_client.go

@@ -33,16 +33,13 @@ func (c restClient) RequestWithContext(ctx context.Context, method string, path
 
 	resp, err := c.client.Do(req)
 	if err != nil {
-		return resp, err
+		return nil, err
 	}
 
 	success := resp.StatusCode >= 200 && resp.StatusCode < 300
 	if !success {
-		err = api.HTTPError{
-			Headers:    resp.Header,
-			RequestURL: resp.Request.URL,
-			StatusCode: resp.StatusCode,
-		}
+		defer resp.Body.Close()
+		return nil, api.HandleHTTPError(resp)
 	}
 
 	return resp, err