Variable font interface doesn't expand

Summary:

When a variable font has more than one axis, it becomes very difficult to tweak the font as the widget doesn't expand.

Steps to reproduce:

• Make sure Interface/Windows/Font selector is set to "List fonts and styles"
• Install a variable font with multiple axes, such as Roboto Flex
• Create a text object in Inkscape
• Open the Text and Font tab
• Select the variable font (e.g. Roboto Flex) and try to adjust the axis values

What happened?

At first, only width is displayed as an option, but after hitting "Apply" the other sliders are there, but very difficult to work with.

What should have happened?

• All the axis sliders should be displayed when the font is selected
• The font_variations widget should expand to at least half the height of the font and text dialog

Version info

Inkscape 1.5-dev (76198da844, 2025-10-23, custom)

                      Compile  (Run)
    GLib version:     2.84.4
    GTK version:      4.18.6 (4.18.6)
    glibmm version:   2.83.1
    gtkmm version:    4.18.0
    libxml2 version:  2.12.10
    libxslt version:  1.1.43
    Cairo version:    1.18.2 (1.18.2)
    Pango version:    1.56.4 (1.56.4)
    HarfBuzz version: 10.4.0 (10.4.0)
    Poppler version:  25.02.0

    OS version:       Fedora Linux 42 (Workstation Edition)