Only focus the undo bar when the focus isn't inside

It should fix the test "must work properly when selecting undo by keyboard"
which calls focus() but it can be steal by fixed callback in setTimeout.

web/editor_undo_bar.js

@@ -105,7 +105,9 @@ class EditorUndoBar {
     // Without the setTimeout, VoiceOver will read out the document title
     // instead of the popup label.
     this.#focusTimeout = setTimeout(() => {
-      this.#container.focus();
+      if (!this.#container.contains(document.activeElement)) {
+        this.#container.focus();
+      }
       this.#focusTimeout = null;
     }, 100);
   }