Log Message:
gtkmm: updated to 3.24.7

3.24.7 (stable):

Gtk:
* Don't derive gtkmm__GtkXxx GTypes from final types
* TextView::get_tabs(): Fix a memory leak

Documentation:
* Widget: Improve the class documentation

Demos:
* Dialog demo: Add a non-modal dialog

Build:
* Meson build: Avoid configuration warnings
* MSVC build: Disable more warnings
* Fix build with -Dbuild-deprecated-api=false

3.24.6 (stable):

Gtk:
* TreeValueProxy: Declare copy constructor =default,
  avoiding warnings from the clang++ compiler
* Object::_release_c_instance(): Unref orphan managed widgets

Demos:
* SizeGroup demo: Set active items in the combo boxes, so something is shown

Build with Meson:
* MSVC build: Support Visual Studio 2022
* Specify 'check' option in run_command()
* Check if Perl is required for building documentation
* Don't use deprecated python3.path() and execute(..., gui_app: ...)