Fix memory leak in settings component

[bluelhf]

According to the plugin verifier, we leak memory in a lambda in SettingsComponent, as a registered Disposable object is never disposed of:

SEVERE - #c.i.o.u.ObjectTree - Memory leak detected: 'fi.testaustime.plugin_intellij.configuration.SettingsComponent$$Lambda$1549/0x00000001012587b8@1c4fc60' of class fi.testaustime.plugin_intellij.configuration.SettingsComponent$$Lambda$1549/0x00000001012587b8 is registered in Disposer but wasn't disposed.
Register it with a proper parentDisposable or ensure that it's always disposed by direct Disposer.dispose call.
See https://jetbrains.org/intellij/sdk/docs/basics/disposers.html for more details.

We should dispose of the resource properly to avoid leaking memory.