Inkscape master: Some themes fail to apply upon restart

Summary:

Particularly the Breeze theme. During testing the other theme that fails to apply is "e17gtk-revolved".

螢幕錄製_20250310_073546

Steps to reproduce:

• open Inkscape
• switch to the Breeze theme
• researt Inkscape
• create a new document or open an existing one

What happened?

The Breeze theme doesn't apply.

What should have happened?

The Breeze theme applies.

Version info

Inkscape 1.5-dev (5eccefde37, 2025-03-07, custom)

                      Compile  (Run)
    GLib version:     2.82.5
    GTK version:      4.16.12 (4.16.12)
    glibmm version:   2.82.0
    gtkmm version:    4.16.0
    libxml2 version:  2.13.6
    libxslt version:  1.1.42
    Cairo version:    1.18.2 (1.18.2)
    Pango version:    1.56.1 (1.56.1)
    HarfBuzz version: 10.4.0 (10.4.0)
    Poppler version:  25.03.0

    OS version:       Slackware 15.0 x86_64 (post 15.0 -current)