[ci] Restrict breathe version at CI

[StrikerRUS]

Recently updated Doxygen at conda-forge results in the following error

Warning, treated as error:
/home/runner/work/LightGBM/LightGBM/docs/C-API.rst:2:Unparseable C cross-reference: '[out]'
Invalid C declaration: Expected identifier in nested name. [error at 0]
  [out]
  ^
make: *** [Makefile:20: html] Error 2

I guess that this is actually breathe issue.

UPD: Well, the root cause was updated breathe, not Doxygen.

[jameslamb]

I feel light we're fighting a long war against CI this last month haha

[StrikerRUS]

breathe has been updated recently too. So more candidates to check...
https://github.com/michaeljones/breathe/releases/tag/v4.29.0

[jameslamb]

thanks for fixing this!

[jameslamb]

I can see that check-docs is passing now, so merging this with admin rights

[StrikerRUS]

Created breathe-doc/breathe#674.

[github-actions]

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