FIX: Ensure required_tag_group is defined on new category records (#20600)

Attaching required tag groups to new categories failed because
`required_tag_group` was undefined on the new category records

This fix sets an empty `required_tag_group` property on the new category
records.

app/assets/javascripts/discourse/app/routes/new-category.js

@@ -32,6 +32,7 @@ export default DiscourseRoute.extend({
       topic_featured_link_allowed: true,
       custom_fields: {},
       search_priority: SEARCH_PRIORITIES.normal,
+      required_tag_groups: [],
     });
   },
 

app/assets/javascripts/discourse/tests/acceptance/category-new-test.js

@@ -8,6 +8,7 @@ import DiscourseURL from "discourse/lib/url";
 import I18n from "I18n";
 import sinon from "sinon";
 import { test } from "qunit";
+import selectKit from "discourse/tests/helpers/select-kit-helper";
 
 acceptance("Category New", function (needs) {
   needs.user();
@@ -21,6 +22,15 @@ acceptance("Category New", function (needs) {
     await fillIn("input.category-name", "testing");
     assert.strictEqual(query(".badge-category").innerText, "testing");
 
+    await click(".edit-category-nav .edit-category-tags a");
+    await click("button.add-required-tag-group");
+
+    const tagSelector = selectKit(
+      ".required-tag-group-row .select-kit.tag-group-chooser"
+    );
+    await tagSelector.expand();
+    await tagSelector.selectRowByValue("TagGroup1");
+
     await click("#save-category");
 
     assert.strictEqual(
@@ -29,6 +39,15 @@ acceptance("Category New", function (needs) {
       "it transitions to the category edit route"
     );
 
+    await click(".edit-category-nav .edit-category-tags a");
+
+    assert.ok(
+      exists(
+        ".required-tag-group-row .select-kit-header[data-value='TagGroup1']"
+      ),
+      "it shows saved required tag group"
+    );
+
     assert.strictEqual(
       query(".edit-category-title h2").innerText,
       I18n.t("category.edit_dialog_title", {