Replace doctests from jacobian_khuri_makdisi.py taking too long time

[kwankyu]

We replace doctest examples in the module sage.rings.function_field.jacobian_khuri_makdisi that are taking too long time with smaller examples.

Before:

sage -t --warn-long 112.9 --random-seed=138126942635581110821969675305757234065 src/sage/rings/function_field/jacobian_khuri_makdisi.py
    [273 tests, 162.67 s]

After:

sage -t --warn-long 113.1 --random-seed=197118826408466343693096609510579001704 src/sage/rings/function_field/jacobian_khuri_makdisi.py
    [272 tests, 122.30 s]

📝 Checklist

• The title is concise and informative.
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• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
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[github-actions]

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[mkoeppe]

LGTM.

[kwankyu]

Thanks!