Add cross-domain-saliency-maps package in related_software. - #13413

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Hey @christodouloskech

It looks to me like CircleCI wants to pre-install any "related software" packages that exist on PyPI, probably so that we can automatically extract the package description and display it on the website. e.g. you can see here that the build docs job executes circleci_dependencies.sh

So adding cross-domain-saliency-maps to this list in circles_dependencies.sh, should resolve the current doc build error.

I added cross-domain-saliency-maps in circlecei_dependences.sh. cross-domain-saliency-maps requires both pytorch and tensorflow. For ease I added the --no-deps flag in pip install, so that installation of tensorflow and pytorch is skipped.

test_plot_volume_source_estimates_on_vol_labels seems to fail the test. Should this be affected by this documentation-only PR?

Only CIs that matter here are style and CircleCI and those look good, as does this page

https://output.circle-artifacts.com/output/job/f9a9569f-6db7-4d84-8eb6-6e08b1305e03/artifacts/0/html/install/mne_tools_suite.html#related-software

Thanks @christodouloskech !

🎉 Congrats on merging your first pull request! 🥳 Looking forward to seeing more from you in the future! 💪