fix(test): Update transactionsList.spec.tsx to await grid cells

[sentry]

The test transactionsList.spec.tsx was failing with TestingLibraryElementError: Unable to find an element by: [data-test-id="grid-cell"].

Root Cause:
The test was calling screen.getAllByTestId('grid-cell') synchronously after await screen.findByTestId('transactions-table'). The transactions-table element (a PanelTable container) is rendered immediately on component mount, even when data is still loading. However, the actual grid-cell elements are rendered asynchronously only after the API data has successfully loaded and the isLoading state transitions to false. This created a race condition where the synchronous getAllByTestId was executed before the grid-cell elements were present in the DOM.

Solution:
Changed screen.getAllByTestId('grid-cell') to await screen.findAllByTestId('grid-cell') in the affected test. This ensures that the test correctly waits for the grid-cell elements to be rendered after the data has loaded, resolving the TestingLibraryElementError. The preceding findByTestId('transactions-table') check is now redundant as a timing gate but can remain for general element presence assertion.

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Fixes JEST-2Y1Z

_{Comment @sentry <feedback> on this PR to have Autofix iterate on the changes.}