Gratnite 6.0.0 removed About dialogs

Prerequisites

[x] I have searched the Issues list for open and closed issues and believe this is a unique, currently unreported bug.

Describe the bug

vocal fails to build with granite 6.0.0 because About dialogs have been removed.

https://github.com/elementary/granite/pull/450

To Reproduce

Steps to reproduce the behavior: Build vocal towards granite 6.0.0

Expected behavior

It should build.

Logs

[  4%] Generating data/com.github.needleandthread.vocal.gresource.c
/build/vocal/src/vocal-2.4.2/src/MainWindow.vala:419.17-419.41: error: The name `show_about' does not exist in the context of `Vocal.VocalApp'
                controller.app.show_about (this);
                ^^^^^^^^^^^^^^^^^^^^^^^^^
Command-line option `--thread` is deprecated and will be ignored
Compilation failed: 1 error(s), 0 warning(s)
make[2]: *** [CMakeFiles/com.github.needleandthread.vocal.dir/build.make:231: com.github.needleandthread.vocal_valac.stamp] Error 1
make[1]: *** [CMakeFiles/Makefile2:127: CMakeFiles/com.github.needleandthread.vocal.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[  4%] Built target i18n
make: *** [Makefile:136: all] Error 2

Platform Information

Please share as many of the following details as possible:

Linux distrubution: Arch Linux
OS version: current
Desktop environment: N/A

Please check the applicable option below:

[x] I'm using a different version (please note here) : 2.4.2

Additional context

We have just removed the About dialog from the Arch package until there is an upstream fix.

https://github.com/archlinux/svntogit-community/commit/03543ffdb6cd52ce1a8293f3303225b3afac2431#diff-3e341d2d9c67be01819b25b25d5e53ea3cdf3a38d28846cda85a195eb9b7203a

VocalPodcastProject / vocal

Gratnite 6.0.0 removed About dialogs #483