gh-search-input throws ember-wormhole error

[kevinansfield]

At some point between 0.8 and master the gh-search-input component has started throwing this error when the dropdown is shown:

Error: The head node of a wormhole must be attached to the DOM

Reproduction steps:

1. Click in the search box
2. Start typing
3. The error will be visible in the console although the dropdown is still shown.

This failing test can be added to core/client/tests/integration/components/gh-search-input.js as the same error is apparent in the tests as well as the application:

it('opens the dropdown on text entry', function () {
    this.render(hbs`{{gh-search-input}}`);
    // enter text to trigger search
    run(() => {
        this.$('input[type="search"]').val('test').trigger('input');
    });
});