Update Adwaita version check for Box unref

As of Adwaita 1.5.0, the GTK Box is not being properly unref'd when the
parent window is closed. Update the conditional to account for this.

Also add a couple of missing unref()s in errdefers.

src/apprt/gtk/Surface.zig

@@ -370,6 +370,7 @@ pub fn init(self: *Surface, app: *App, opts: Options) !void {
 
     // Create an overlay so we can layer the GL area with other widgets.
     const overlay = gtk.Overlay.new();
+    errdefer overlay.unref();
     const overlay_widget = overlay.as(gtk.Widget);
     overlay.setChild(gl_area_widget);
 

src/apprt/gtk/Tab.zig

@@ -64,6 +64,7 @@ pub fn init(self: *Tab, window: *Window, parent_: ?*CoreSurface) !void {
     // box makes it easier to maintain the tab contents because we never need to
     // change the root widget of the notebook page (tab).
     const box = gtk.Box.new(.vertical, 0);
+    errdefer box.unref();
     const box_widget = box.as(gtk.Widget);
     box_widget.setHexpand(1);
     box_widget.setVexpand(1);

src/apprt/gtk/TabView.zig

@@ -209,14 +209,11 @@ pub fn closeTab(self: *TabView, tab: *Tab) void {
 
     // If we have no more tabs we close the window
     if (self.nPages() == 0) {
-        // libadw versions <= 1.3.x leak the final page view
+        // libadw versions < 1.5.1 leak the final page view
         // which causes our surface to not properly cleanup. We
         // unref to force the cleanup. This will trigger a critical
         // warning from GTK, but I don't know any other workaround.
-        // Note: I'm not actually sure if 1.4.0 contains the fix,
-        // I just know that 1.3.x is broken and 1.5.1 is fixed.
-        // If we know that 1.4.0 is fixed, we can change this.
-        if (!adwaita.versionAtLeast(1, 4, 0)) {
+        if (!adwaita.versionAtLeast(1, 5, 1)) {
             const box: *gtk.Box = @ptrCast(@alignCast(tab.box));
             box.as(gobject.Object).unref();
         }