🐛 Remove extra padding in alert dialog

[edwardaux]

Description

This one is a minor UI glitch, but I don't have time to raise a PR at the moment (it'd be a good one for any new contributors)... when the suppress flag is set to null in the alert dialog, we end up with two SizedBox widgets in a row (which increases the padding at the bottom under the button).

This first SizedBox should be included in the if condition here

ie. it should look something like (untested):

if (suppress != null) ...[
  const SizedBox(height: 16),
  DefaultTextStyle(
    style: MacosTheme.of(context).typography.headline,
    child: suppress!,
  ),
],
const SizedBox(height: 16),

Steps To Reproduce

Show a MacosAlertDialog where suppress is set to null