main: Fix syncing animations-enabled

Whether or not animations should be enabled depends on various
factors, some of which may change at runtime. We therefore
track changes, and sync the setting by calling inhibit/uninhibit
as necessary.

Except that we never actually record the new state, so when animations
are disabled, we end up inhibiting them every time
the setting is synced, whoops.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2698>

js/ui/main.js

@@ -963,6 +963,7 @@ var AnimationsSettings = class {
         const shouldEnableAnimations = this._shouldEnableAnimations();
         if (this._animationsEnabled === shouldEnableAnimations)
             return;
+        this._animationsEnabled = shouldEnableAnimations;
 
         const settings = St.Settings.get();
         if (shouldEnableAnimations)