fix: check for closeable() before calling in spatialnavigation (#8832)

## Description
Passing the back key causes an error in spatial navigation if the event
target does not have a `closeable` function.

## Specific Changes proposed
Add a check before calling.

src/js/spatial-navigation.js

@@ -120,7 +120,8 @@ class SpatialNavigation extends EventTarget {
       const action = SpatialNavKeyCodes.getEventName(actualEvent);
 
       this.performMediaAction_(action);
-    } else if (SpatialNavKeyCodes.isEventKey(actualEvent, 'Back') && event.target && event.target.closeable()) {
+    } else if (SpatialNavKeyCodes.isEventKey(actualEvent, 'Back') &&
+        event.target && typeof event.target.closeable === 'function' && event.target.closeable()) {
       actualEvent.preventDefault();
       event.target.close();
     }