Replace fmt.Errorf(\"%s\", detail) with errors.New in checkImageBuildResponse

fmt.Errorf with a plain %s verb (no wrapping) triggers go vet's
printf-style warning and adds unnecessary overhead. errors.New is the
correct call when there is no cause to wrap.

ai-assisted=yes

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: rizwanreza

internal/test/container.go

@@ -518,7 +518,7 @@ func checkImageBuildResponse(body io.ReadCloser, logOutput io.Writer) error {
 			if msg.ErrorDetail.Message != "" {
 				detail = msg.ErrorDetail.Message
 			}
-			return fmt.Errorf("%s", detail)
+			return errors.New(detail)
 		}
 	}
 	return nil