[CI] Skip flaky download tests in PR CI

[DN6]

What does this PR do?

We have a couple of flaky tests related to the number of GET requests being performed when fetching a model. The issue only seems to happen in the when the test is triggered via CI and it is not reproducible when SSHing into the runner and running the same tests or the entire test suite.

Since we're migrating to new runner groups soon, let's skip these tests for now and re-enable with the new machines to see if it fixes it.

Fixes # (issue)

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[sayakpaul]

But even when sshd into the runner I am unable to reproduce the error though:

and it reproducible when SSHing into the runner and running the same tests

[DN6]

@sayakpaul sorry meant to say "not reproducible". Updated the description.

[sayakpaul]

Might be also nice to check what we discussed in https://huggingface.slack.com/archives/C02V5EA0A95/p1721630115211789