`Doc/library/turtle.rst` doctests are failing when `tkinter` is not present

[sobolevn]

Bug report

There are multiple places where :skipif: _tkinter is None is missing. So, local builds are failing with something like:

Document: library/turtle
------------------------

Warning, treated as error:
**********************************************************************
File "library/turtle.rst", line 2797, in default
Failed example:
    for turtle in turtles():
         turtle.reset()
Exception raised:
    Traceback (most recent call last):
      File "/Users/sobolev/Desktop/cpython2/Lib/doctest.py", line 1374, in __run
        exec(compile(example.source, filename, "single",
      File "<doctest default[0]>", line 1, in <module>
        for turtle in turtles():
                      ^^^^^^^
    NameError: name 'turtles' is not defined

make[1]: *** [build] Error 2
Testing of doctests in the sources finished, look at the results in build/doctest/output.txt
make: *** [doctest] Error 1

I have a PR ready.

Linked PRs

• gh-111735: Fix turtle.rst doctests when tkinter is not present #111736
• gh-111735: Skip turtle doctests when _tkinter is not available #156417