Draft: E2E tests: refresh on diffs page of MR

What does this MR do and why?

Since diffs are now being loaded async the E2E tests in the master pipeline seem to be navigating to the Changes tab before they are available. This causes a 404 and a never ending spinner on the page, then the tests fail. #396649 (closed)

This MR waits for the file tree icon to be available in the Changes tab and refreshes the page if not. This ensures that the diff is available.

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