Fix Read the Docs build errors

[shinyaaa]

I have just noticed that Read the Docs has been failing to build for about a year.
The following are the areas that need to be changed.

• .readthedocs.yaml needs to exist in the repository root (https://blog.readthedocs.com/migrate-configuration-v2/)
• PyYAML installation errors need to be addressed (Error installing Pyyaml==5.4, Cython_sources yaml/pyyaml#724 (comment))

[michaelpq]

Thanks for the patch? How it is possible to check its validity? I don't have an access to the read-the-doc build. @yamatattsu , could you comment?

[shinyaaa]

@michaelpq OK, thanks!

@yamatattsu @SeinoYuki Could you review this?

Build failed.

Successful build of the document in the repository forked for testing.

[SeinoYuki]

Thanks for the patch.
I checked build of the Read the Docs.
I think this PR is no problem.

[SeinoYuki]

back patch committed by 6c308e9, f811176, d15793c, 028f0c5

[shinyaaa]

I confirmed that the document builds of all branches have succeeded. Thank you!