Fix deprecated code warning

[Mantas-2155X]

Fixes file:///usr/share/sddm/themes/materia-dark/Main.qml:31:5: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }

[varlesh]

It's can be compability on LTS distros with old Qt versions? On Elarun not use this functions: https://github.com/sddm/sddm/blob/develop/data/themes/elarun/Main.qml#L42

[Mantas-2155X]

I believe this functionality was added with Qt 5.14 as seen here.

[Mantas-2155X]

Kubuntu 22.04 LTS has Qt 5.15.3, Kubuntu 20.04 LTS has Qt 5.12.8

so I guess it is not compatible on older LTS releases :(

[varlesh]

Ok, thx! I think now it's can not be merged... but not close, for future