Fix a TypeScript conformance check

Promises have to be awaited.

Change-Id: I2aa2fd6cdf8a4fc5c7780578dd5306290cb3fa43
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
index aa5a328..85a3623 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
@@ -1126,7 +1126,7 @@
   private async openDeleteCommentOverlay() {
     this.showConfirmDeleteOverlay = true;
     await this.updateComplete;
-    this.confirmDeleteOverlay?.open();
+    await this.confirmDeleteOverlay?.open();
   }
 
   private closeDeleteCommentOverlay() {