[ci] fix R linting job (fixes #3873)

[jameslamb]

Attempting to fix #3873.

Warning message:
package ‘lintr’ was built under R version 3.6.3
[1] 49 R files need linting
Error in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]) :
namespace ‘xfun’ 0.15 is being loaded, but >= 0.19 is required
Calls: ... namespaceImportFrom -> asNamespace -> loadNamespace
Execution halted

There might be a mistake somewhere in lintr's feedstock on conda-forge or in one of its dependencies. {xfun} is not a direct dependency of {lintr} (https://github.com/conda-forge/r-lintr-feedstock/blob/master/recipe/meta.yaml), so it must be a dependency of a dependency (or deeper 😆 ). For now, I'm just going to try forcing conda install to get a newer version.

[jameslamb]

It seems like this fix did fix the lint job! https://github.com/microsoft/LightGBM/pull/3877/checks?check_run_id=1785176162

[StrikerRUS]

Thanks!

[StrikerRUS]

Should we report this in conda-forge repo?

[jameslamb]

Should we report this in conda-forge repo?

yes, I will

[jameslamb]

should we report this in the conda-forge repo

Created conda-forge/r-lintr-feedstock#12

[jameslamb]

It seems that lint is passing, and all other CI jobs are passing except the ones we know are broken and waiting on other PRs (#3876 (comment)), so I'm going to merge this.

[StrikerRUS]

@jameslamb

Created conda-forge/r-lintr-feedstock#12

Thank you very much! Hope this will allow us revert the workaround eventually.

[github-actions]

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