[ci][docs] downdrage sphinx and fix LaTeX error in R-package tests

[StrikerRUS]

Fixed #2974.

While we are waiting new breathe release which will be compatible with sphinx 3, let's downgrade sphinx version to fix our CI.
Refer to breathe-doc/breathe#491.

[jameslamb]

Thank you! I had a feeling this would have to be the answer :/

[jameslamb]

😱 oh no

[StrikerRUS]

This PR is facing the same issue #2976 (comment). I think we should extract workaround from @henry0312's PR to make it clean.

[jameslamb]

oh nice ok! @henry0312 you can ignore https://github.com/microsoft/LightGBM/pull/2976/files#r404111998, we'll just bundle it into this PR

[jameslamb]

I'm good with the R changes, merge whenever it builds

[henry0312]

I have no idea about /Library/TeX/texbin/tlmgr: unexpected return value from verify_checksum: -5
https://dev.azure.com/lightgbm-ci/lightgbm-ci/_build/results?buildId=5753&view=logs&j=2e42d92c-6989-5c5a-9adb-4d8d43874989&t=7c5d831f-c13d-5c19-c317-c20b1d55f3d3&l=75

[jameslamb]

@StrikerRUS since this is blocking other PRs, I think we should do this:

if [[ $OS_NAME == "macos" ]]; then
    R CMD check ${PKG_TARBALL} \
        --no-manual \
    || exit -1
else
    R CMD check ${PKG_TARBALL} \
        --as-cran \
    || exit -1
fi

Then I can work on fixing it today, but other PRs will be unblocked

[StrikerRUS]

@jameslamb

since this is blocking other PRs, I think we should do this:

As other PRs are not urgent (maintaince or new feature related), I believe they can wait while we are fixing this error.

[jameslamb]

@jameslamb

since this is blocking other PRs, I think we should do this:

As other PRs are not urgent (maintaince or new feature related), I believe they can wait while we are fixing this error.

I'm ok with that. If they become more urgent, just know I'm ok with that temporary solution.

[StrikerRUS]

Just reverted tlmgr-related changes as it is "every year" problem and we have nothing to do with it. Refer to #2976 (comment).

Last year they fixed it in the same day.

[StrikerRUS]

OK, as it was suggested in maillist, I added --verify-repo=none option to install all needed stuff.

[StrikerRUS]

Merging this to unblock all waiting PRs.

[github-actions]

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