using # needs in posets folder

[fchapoton]

using the needs directive in posets folder

📝 Checklist

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

[fchapoton]

better now ?

[mkoeppe]

File "sage/combinat/posets/posets.py", line 3719, in sage.combinat.posets.posets.FinitePoset.Integer
Failed example:
    needs sage.groups sage.libs.flint
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 1142, in compile_and_execute
        compiled = compiler(example)
      File "/sage/src/sage/doctest/forker.py", line 676, in compiler
        code = compile(example.source, filename, "single",
      File "<doctest sage.combinat.posets.posets.FinitePoset.Integer[0]>", line 1
        needs sage.groups sage.libs.flint
              ^
    SyntaxError: invalid syntax
**********************************************************************
File "sage/combinat/posets/posets.py", line [37](https://github.com/sagemath/sage/actions/runs/5978963391/job/16222089762?pr=36114#step:14:38)37, in sage.combinat.posets.posets.FinitePoset.Integer
Failed example:
    needs sage.groups sage.libs.flint
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 1142, in compile_and_execute
        compiled = compiler(example)
      File "/sage/src/sage/doctest/forker.py", line 676, in compiler
        code = compile(example.source, filename, "single",
      File "<doctest sage.combinat.posets.posets.FinitePoset.Integer[8]>", line 1
        needs sage.groups sage.libs.flint
              ^
    SyntaxError: invalid syntax

needs needs #

[github-actions]

Documentation preview for this PR (built with commit b42148c; changes) is ready! 🎉

[mkoeppe]

LGTM. Thanks