message: Fix detection of `--json future-incompat`
diff: @@ -183,7 +183,9 @@ impl TargetInfo {
  let supports_json_future_incompat = rustc
  .cached_output(
  - process.clone().arg("--json").arg("future-incompat"),
  + process
  + .clone()
  + .args(&["--error-format", "json", "--json", "future-incompat"]),
  extra_fingerprint,
  )
  .is_ok();
  