[MRG] add tests for R conda

[aplamada]

It simply adds tests for R 3.6, 4.0 and 4.1 using conda.

This is a follow up of the closed PR #1086 .
The structure for the tests is as in #1104 .

@yuvipanda Can you please have a look at this new PR?

[yuvipanda]

@aplamada thanks for making these! Any idea why they are failing?

[aplamada]

@yuvipanda Thanks!
It is not possible to satisfy all dependencies (see below).

Looking for: ['r-base=4.1', 'r-irkernel=1.1', 'r-devtools']
  
Encountered problems while solving.
Problem: package r-irkernel-1.1-r35h6115d3f_0 requires r-base >=3.5,<3.6.0a0, but none of the providers can be installed

Previously it used to downgrade the R version (see here).

[yuvipanda]

ahhh. I don't really know enough about conda to know how to fix it tho :|

[manics]

@yuvipanda Do we need to pin the version of r-irkernel? Can we rely on the conda solver to automatically install a compatible version of r-irkernel for whatever r-base version is requested?

repo2docker/repo2docker/buildpacks/conda/__init__.py

Line 359 in 4352535

mamba install -p {0} r-base{1} r-irkernel=1.2 r-devtools -y && \

[aplamada]

@manics @yuvipanda the new version r-irkernel=1.2 works fine with all conda R tests.

[manics]

Thanks!

[welcome]

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