Container for group item count still visible if display count is off

**Cosmetic bug:**
When the display of group item counts is deactivated in the settings, the enclosing darkgrey rectangles are still visible in the group panel.

![grafik](https://github.com/JabRef/jabref/assets/7942719/8358d251-5766-4b6d-a687-b0e9cee33e12)
