Sped up tests that use {{liquid-if}}

no issue

- some tests were unnecessarily slowed down by waiting repeatedly for animations to complete
- added override for `<LiquidContainer>` component that `<LiquidIf>` uses internally with the only change being to set the default growth animation duration to 5ms when running tests

ghost/admin/app/components/liquid-container.js

@@ -0,0 +1,12 @@
+import LiquidContainer from 'liquid-fire/components/liquid-container';
+import config from 'ghost-admin/config/environment';
+
+export default LiquidContainer.extend({
+    init() {
+        this._super(...arguments);
+
+        if (config.environment === 'test') {
+            this.growDuration = 5;
+        }
+    }
+});