Missing animation when clicking the search button in the headerbar

[SeaDve]

Version

Alternative toolbar 0.18.4 Rhythmbox version 3.4.4 Gnome 3.38 Fedora 33 Workstation

How to reproduce:

1. Launch rhythmbox with the plugin enabled
2. Click the search button in the header bar
3. Click the search button again to hide the search bar

What happened

There is no animation

What should happen

There should be animation when search bar is hiding