E2E: Skip bulk import UI spec on slow network connection

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I was not able to reproduce the issue manually with same throttling settings which leads me to believe it's some strange intermittent test issue.

Gitlab to Gitlab migration is a very administrative task, so I doubt it's a valid usecase to perform it on a 32kb/s connection with additional 2s of latency, so just setting this test to be skipped on a slow network configuration.

Closes: #340903 (closed)

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