Logo animation on the main page can be duplicated

See:
![image](https://github.com/ruffle-rs/ruffle-rs.github.io/assets/288816/446c46d0-644f-4ba9-ab51-8a7fab5ade47)

To reproduce:
 - Open https://ruffle.rs
 - Switch to a different tab (such as "Downloads" or "Compatibility")
 - Switch back to "About Ruffle"
 
 Probably caused by https://github.com/ruffle-rs/ruffle-rs.github.io/pull/232.
 
 Tested in both Firefox and Chrome.