Fix: bump Isar dependency to a version supporting 32-bit Android devices

There is an issue in libmdbx which prevents Isar versions before 2.4.0 to run on 32-bit ARM devices: https://github.com/isar/isar/issues/187. Additionally another error was introduced with Isar version 2.5.0 having a similar effect: https://github.com/isar/isar/issues/398. This currently results in a black screen when running Fun With Kanji on any 32-bit ARM Android device. When depending on version 2.4.0 I can successfully start the app on my 32-bit phone. According to the comments on the second issue linked, version 3.0.0 should work on 32-bit ARM, too. But there is not yet a stable release for that version. This MR bumps the version of Isar to 2.4.0 and rebuilds the auto-generated Isar schemas.