deskutils/maliit-keyboard: update to 2.3.0

Changelog:

• Add CI build rule to build on KDE Neon
• Remove unused window flag setting code
• Replace remaining context properties with singletons
• Remove unused and useless install target
• Fix builds without Pinyin
• Fix the build of unit tests and enable them by default
• Fix a possible undefined error in CharKey
• Improve the PhoneNumber keyboard layout
• Fix the settings URL for Plasma Mobile kcm renaming
• Use new syntax for Connections components
• Rely on QQC2 styles insted of an internal themes implementation