Text kerning changable when it should be impossible

Summary:

Since kerning seems to be impossible in SVG2 flowtext it should not be possible to change the values via shortcuts either. A CLEAR notification is needed that this restriction (bug!) exists. Just graying out the buttons is not enough, as it is very easy to not notice buttons when you don't use the GUI. On top of that the shortcut actually changes the values, adding to the confusion. It took me an ANNOYINGLY long amount of time and effort to find this out.

@KrIr17 advised to create this issue on #9151 (comment 2583157502)

Steps to reproduce:

• open Inkscape
• create a flowtext object and add some characters
• start kerning them with alt+arrow keys

What happened?

• nothing happens
• values in greyed out buttons change

What should have happened?

– a big video should pop up, rickrolling with the volume maxed out!

• or text should get kerned
• or maybe a warning message should pop up?

Sample attachments:

Kooha-2025-06-22-22-28-56

Version info

Inkscape 1.4.2 (ebf0e940d0, 2025-05-08)

                      Compile  (Run)
    GLib version:     2.84.1
    GTK version:      3.24.49 (3.24.49)
    glibmm version:   2.66.1
    gtkmm version:    3.24.5
    libxml2 version:  2.13.6
    libxslt version:  1.1.42
    Cairo version:    1.18.4 (1.18.4)
    Pango version:    1.56.3 (1.56.3)
    HarfBuzz version: 9.0.0 (9.0.0)

    OS version:       GNOME 48 (Flatpak runtime)