[nextest-runner] close stdin while running list commands

No reason to have stdin open for these.

nextest-runner/src/list/test_list.rs

@@ -690,8 +690,9 @@ impl<'g> RustTestArtifact<'g> {
  &self.package,
  &self.non_test_binaries,
  );
- // Capture stdout and stderr.
+ // Capture stdout and stderr, and close stdin.
  cmd.command_mut()
+ .stdin(std::process::Stdio::null())
  .stdout(std::process::Stdio::piped())
  .stderr(std::process::Stdio::piped());