Added File Browser header icons span two rows

[matthewgasbarro]

Description

With the jupyterlab-git extension enabled, the Git Clone icon is added as the last icon in the File Browser header, but when JupyterLab is loaded, the default File Browser width places the icon on a second row. Resizing it allows the icons to appear in a single row, but the computation for minimum or default width should accommodate the extra icons as was the case in JupyterLab 3.

Reproduce

1. Install jupyterlab-git
2. Open JupyterLab
3. Notice the Git Clone icon is on a second row
   

Expected behavior

The Git Clone icon should be the last icon in one row

Context

Operating System and version: Windows 10
Browser and version: Chrome Version 123
JupyterLab version: 4.1.5

[krassowski]

Related to #14125.