GitHub-Actions: Add a simple test that checks if all packages specified in the .yml file were also installed in the conda environment

[JohannesWiesner]

First run tcy.py to create an input .yml file, create an environment from that file and then try to import all modules that appear in the input .yml file

This could be possibly done with: python -c "import nilearn nipype ...."

See: https://github.com/mamba-org/setup-micromamba#usage

[JohannesWiesner]

Another way to test if all packages that were specified in .tsv file were installed, is to run micromamba list. This list has to be reduced to only packages that can be found in .tsv file (possibily using grep?). Then export this to .csv and use pandas to check that all packages that appear in .tsv file also appear in micromamba environment.

[JohannesWiesner]

But see this issue, we have to use the workaround with

conda list -p "${MAMBA_ROOT_PREFIX}/envs/${{ matrix.os }}" --explicit > ./environments/${{ matrix.os }}_solved.txt

Only this gets us a list with conda + pip packages. This command is already used so we don't need to execute it another time. But we somehow have to bring it into a format that allows us to compare it to the input .yml file.