FIX: DButton ellipsis argument (#19640)

This regressed in a8890295

app/assets/javascripts/discourse/app/templates/components/d-button.hbs

@@ -32,7 +32,7 @@
   {{~#if this.computedLabel~}}
     <span class="d-button-label">
       {{~html-safe this.computedLabel~}}
-      {{~#if this.ellipsis~}}
+      {{~#if @ellipsis~}}
         &hellip;
       {{~/if~}}
     </span>

app/assets/javascripts/discourse/tests/integration/components/d-button-test.js

@@ -312,4 +312,10 @@ module("Integration | Component | d-button", function (hooks) {
 
     assert.strictEqual(this.foo, "bar");
   });
+
+  test("ellipses", async function (assert) {
+    await render(hbs`<DButton @translatedLabel="test label" @ellipsis=true />`);
+
+    assert.dom(".d-button-label").hasText("test label…");
+  });
 });