http: do not use buffer when draining and discarding http body

Use io.Copy with io.Discard instead of io.ReadAll to drain the whole http body
when an error occurred.

This does not write the body unnecessary to a buffer in memory that will never
be used.

internal/jenkins/client.go

@@ -99,7 +99,7 @@ func (c *Client) do(method, url string, result interface{}) error {
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		_, _ = io.ReadAll(resp.Body)
+		_, _ = io.Copy(io.Discard, resp.Body)
 		return &ErrHTTPRequestFailed{Code: resp.StatusCode}
 	}