Log Message:
gtkmm3: updated to 3.24.9

3.24.9 (stable):

Documentation:
* Gtk::Clipboard: Update documentation
* Gtk::ScrolledWindow: Update the class description

Tests:
* Gdk::RGBA test: Avoid some comparisons for exact equality

Meson build:
* Donʼt fail if warning_level=everything

3.24.8 (stable):

Gtk:
* gtk/gtkmm/base.h: Fix GTK_VERSION_GT_MICRO

Documentation:
* Remove README.SUN and other obsolete files

Build with Meson:
* Detect if we build from a git subtree
* Fix the evaluation of is_git_build on Windows
* Don't copy files with configure_file()