Update the theme to be in sync with other Xfce changes.

- Prevent Unity desktop theme from being installed
Added disable-unity_v3.23.1.patch

- Update to version 3.23.1+git1.77c0887:
* Cleanup leftovers and correct emerald file mistakinly being renamed

- Update to version 3.23.1+git0.a96e825:
* Sync with Greybird 3.23.1
* Add initial support for Gtk4 and libhandy
* Fix dark xfwm4-a11y install path
* Fix xfwm4-a11y and xfwm4-compact install path
* Fix: GtkLabel: Backdropped selection color adjusted
* Fix: Backdropped selection: GtkListBoxes weren't grey
* Hotfix: removed background color for non-bg items
* Gtk3: Adjusted selected backdrop fg/bg colors: shades of grey.
* Changes the xfwm4 border colors
* build: refactor meson
* Correct gradients for horizontal scrollbars
* Reduce messagedialog buttonbox size
* Make CSD titlebars slimmer
* Correct gradients for horizontal scrollbars (shimmerproject/Greybird#288)
* Greybird-Dark titlebar decorations now match their CSD counterparts (shimmerproject/Greybird#301)
* Background selection colors are now grey instead of blue for better readability
* Add initial support for Gtk4 and libhandy
* Install index.theme