Fix an occurrence of lazy_import

[user202729]

Previously the following code fails if executed right after Sage starts:

P.<x,y,z> = ProjectiveSpace(QQ, 2)
C = Curve([(x^2 + y^2 - y*z - 2*z^2)*(y*z - x^2 + 2*z^2)*z + y^5], P)
C.ordinary_model()

The error is:

NotImplementedError: object does not support iteration

This pull request fixes it. The reason why it is fixed is explained in the code edit.

📝 Checklist

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⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit fc26616; changes) is ready! 🎉
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[JosePisco]

Works as intended on my end (version 10.7.beta9). Thanks for the fix.

[JosePisco]

I don't have the permission to change labels, someone else will have to do it.