✅(e2e) reduce flakinees

- Because of parallel test execution, some tests
were flaky when using goToGridDoc, the title
changed between the time we got the document list
and the time we clicked on the document.
- Improve addChild function.

src/frontend/apps/e2e/__tests__/app-impress/doc-trashbin.spec.ts

@@ -102,6 +102,7 @@ test.describe('Doc Trashbin', () => {
       page,
       browserName,
       docParent: subDocName,
+      docName: 'my-trash-editor-subsubdoc',
     });
     await verifyDocName(page, subsubDocName);