fix the 2 broken linters

[fchapoton]

This repairs the two broken linters.

📝 Checklist

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

[dcoudert]

I assume it should be x^{prec} here.

[fchapoton]

voilà, voilà

[dcoudert]

failing doctest

sage -t --long --random-seed=286735480429121101562228604801325644303 sage/dynamics/arithmetic_dynamics/dynamical_semigroup.py
**********************************************************************
File "sage/dynamics/arithmetic_dynamics/dynamical_semigroup.py", line 933, in sage.dynamics.arithmetic_dynamics.dynamical_semigroup.DynamicalSemigroup.__mul__
Failed example:
    f*g
Expected:
    Traceback (most recent call last):
    ...
    TypeError: can only multiply dynamical semigroups with other dynamical semigroups of the same type
Got:
    <BLANKLINE>
    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.dynamics.arithmetic_dynamics.dynamical_semigroup.DynamicalSemigroup.__mul__[46]>", line 1, in <module>
        f*g
        ~^~
      File "/sage/src/sage/dynamics/arithmetic_dynamics/dynamical_semigroup.py", line 967, in __mul__
        raise ValueError("left dynamical semigroup's domain must equal right dynamical semigroup's codomain")
    ValueError: left dynamical semigroup's domain must equal right dynamical semigroup's codomain
**********************************************************************
1 item had failures:
   1 of  62 in sage.dynamics.arithmetic_dynamics.dynamical_semigroup.DynamicalSemigroup.__mul__
    [398 tests, 1 failure, 5.31 s]

[EnderWannabe]

Changes look good to me.

[github-actions]

Documentation preview for this PR (built with commit 3bf709c; changes) is ready! 🎉

[dcoudert]

LGTM.