[CI] Fix TRANSFORMERS_FLAX_WEIGHTS_NAME import issue

[DN6]

What does this PR do?

Latest version of transformers on main has removed FLAX_WEIGHTS_NAME from transformers.utils. Our CI is currently failing because of this.

Since we've just deprecated Flax, we need to version guard transformers, and weights based on the last supported version.

Fixes # (issue)

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[yiyixuxu]

thanks!

[sayakpaul]

Sweet!

[sayakpaul]

Some Kandinsky tests started failing which I don't think it related to this PR.