Fluid Density and Gravity Panels don't have a max width when mystery item is selected

[Nancy-Salpepi]

Test device
MacBook Air M1 chip

Operating System
14.6.1

Browser
Safari 17.6

Problem description
For phetsims/qa#1141 and possibly related to changes made in #361, with ?stringTest=dynamic and a mystery fluid/planet selected, pressing the right arrow multiple times causes the panels to continually expand and overlap one another.

Steps to reproduce

1. Add ?stringTest=dynamic to the end of the Buoyancy url
2. Go to the Lab Screen and select Fluid A
3. Press the right arrow key several times
4. Repeat with Planet X selected in the Gravity panel

Visuals