Fix: `Ui::new_child` does not consider the sizing_pass field of `UiBuilder`

[zhatuokun]

During the sizing pass we want widgets to use up as little space as possible, but it does not consider the sizing_pass field of UiBuilder.

[github-actions[bot]]

Preview available at https://egui-pr-preview.github.io/pr/5262-fix-layout-sizing-pass Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

[emilk]

Good catch!