windowplacment: Use correct GTK4 property for maximization
"is-maximized" was renamed to "maximized" for GTK4, an oversight during porting.
Listen to "maximized" instead.
Fixes #582 (closed)
"is-maximized" was renamed to "maximized" for GTK4, an oversight during porting.
Listen to "maximized" instead.
Fixes #582 (closed)