gh-101100: Fix sphinx warnings in turtle.rst

[sobolevn]

It was:

/Users/sobolev/Desktop/cpython/Doc/library/turtle.rst:2318: WARNING: py:class reference target not found: tkinter.Canvas
/Users/sobolev/Desktop/cpython/Doc/library/turtle.rst:2333: WARNING: py:class reference target not found: tkinter.Canvas
/Users/sobolev/Desktop/cpython/Doc/library/turtle.rst:2415: WARNING: py:class reference target not found: tkinter.Canvas
/Users/sobolev/Desktop/cpython/Doc/library/turtle.rst:2421: WARNING: py:class reference target not found: tkinter.Canvas

But, since tkinter.Canvas is not documented in tkinter, we cannot reference it.

• Issue: Fix all Sphinx reference warnings in the documentation #101100

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📚 Documentation preview 📚: https://cpython-previews--109394.org.readthedocs.build/

[AlexWaygood]

Perhaps a better fix might be just to document tkinter.Canvas in the tkinter docs? I don't know much about tkinter, though,so maybe there's a reason why it's not documented currently :)

[terryjreedy]

Looks right given the current state of tkinter docs. The tkinter widget docs were referred to external sources. Only the ttk widget are documented (and with a few error as I remember). This should be fixed, and there may be an issue, but it will be a big project to do right.

[miss-islington]

Thanks @sobolevn for the PR, and @terryjreedy for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-109416 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-109417 is a backport of this pull request to the 3.11 branch.

[terryjreedy]

If and when the tk widgets are documented, I (we) should hopefully remember to search .rst files for '!tkinter' to see where the '1' can/should be removed.