some ruff auto-fixes in schemes + error links in doc

[fchapoton]

Some fixes made by ruff in the schemes folder (codes C4, UP02, UP009)

plus adding manually some links to errors in the doc

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.

[mkoeppe]

Otherwise LGTM

[mkoeppe]

https://github.com/sagemath/sage/actions/runs/7195279189/job/19597658375?pr=36870#step:14:73

File "src/sage/schemes/curves/affine_curve.py", line 1840, in sage.schemes.curves.affine_curve.AffinePlaneCurve_field.braid_monodromy
Failed example:
    C.braid_monodromy()               # optional - sirocco
Exception raised:
    Traceback (most recent call last):
      File "/sage/src/sage/doctest/forker.py", line 709, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/sage/src/sage/doctest/forker.py", line 1144, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.schemes.curves.affine_curve.AffinePlaneCurve_field.braid_monodromy[2]>", line 1, in <module>
        C.braid_monodromy()               # optional - sirocco
        ^^^^^^^^^^^^^^^^^^^
      File "sage/misc/cachefunc.pyx", line 2329, in sage.misc.cachefunc.CachedMethodCallerNoArgs.__call__
        self.cache = f(self._instance)
      File "/sage/src/sage/schemes/curves/affine_curve.py", line 1[85](https://github.com/sagemath/sage/actions/runs/7195279189/job/19597658375?pr=36870#step:14:86)4, in braid_monodromy
        return braid_monodromy(f)[0]
               ^^^^^^^^^^^^^^^^^^
      File "/sage/src/sage/schemes/curves/zariski_vankampen.py", line 1206, in braid_monodromy
        disc = discrim(glist)
               ^^^^^^^^^^^^^^
      File "/sage/src/sage/schemes/curves/zariski_vankampen.py", line 214, in discrim
        h0 = u[1].radical()
             ^^^^^^^^^^^^
    AttributeError: 'str' object has no attribute 'radical'

Also:
sage -t --long --random-seed=286735480429121101562228604801325644303 sage/schemes/curves/zariski_vankampen.py # 15 doctests failed

[github-actions]

Documentation preview for this PR (built with commit a5cd340; changes) is ready! 🎉

[mkoeppe]

LGTM