test(frontend): await the userEvent calls that needed restructuring - #44799

SUMMARY

#43512 made every @testing-library/user-event API asynchronous. #44315, #44323 and #44335 awaited the calls that needed only a mechanical await, and deliberately left seven call sites out because awaiting them in place would not have been correct. This PR finishes those seven (details in #44798). Each needs a different fix:

RowCountLabel.test.tsx (4 sites), four synchronous tests hovered and then asserted immediately, so the assertion ran before the hover was dispatched and could not observe it; the tests would pass with the hover deleted. They become async and await the hover. The expectation itself is unchanged and still correct: RowCountLabel renders a Tooltip only when limitReached, which is false in all four.

Home.test.tsx, Footer.test.tsx (1 site each), both had an un-awaited click inside a waitFor callback, which waitFor retries, making the click fire-and-forget and possibly repeated. The click is lifted out and awaited, leaving only the assertion inside waitFor. In Footer.test.tsx the surrounding waitFor is replaced by findByText, which is what it was emulating.

SqlEditorTabHeader.test.tsx (1 site, 12 callers), the openTabDropdown helper was synchronous, so all 12 tests asserted against a dropdown whose opening click had not been dispatched. The helper becomes async and every call site awaits it. All 12 enclosing tests were already async, so no test signature changes.

No assertions were weakened, no timeouts widened, no retries added, and no production code is touched.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A: test-only change.

TESTING INSTRUCTIONS

cd superset-frontend
npm run test -- \
  src/components/RowCountLabel/RowCountLabel.test.tsx \
  src/pages/Home/Home.test.tsx \
  src/features/datasets/AddDataset/Footer/Footer.test.tsx \
  src/SqlLab/components/SqlEditorTabHeader/SqlEditorTabHeader.test.tsx

All 43 tests across the 4 suites pass. oxlint and oxfmt --check are clean on the changed files, and tsc --noEmit over the whole superset-frontend project reports no errors.

ADDITIONAL INFORMATION

• Has associated issue: Fixes Seven un-awaited userEvent call sites remain after the user-event v14 migration #44798
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API