Add neotest jump last

[MisanthropicBit]

I often find myself wanting to jump back to the test that was last run. I could add a mark but I forget sometimes.

Other fixes:

• ubuntu-20.04 is deprecated which caused the docgen workflow to not run. Therefore this PR will include unrelated documentation updates.
• Bumped all actions to most recent versions. This also caused the docgen workflow to not run.
• Wrapped a call to nvim_create_autocmd in vim.schedule as it triggers the cannot be called in a fast event occasionally.
• Added a space before the --- docstring description of neotest.jump.prev as the docgen script doesn't seem to parse it otherwise.

The docgen workflow is still failing with E5113: Error while calling lua chunk: ./scripts/gendocs.lua:4: module 'neotest.utils' not found:. I'll look into that. The workflow is also using a very old version of neovim (v0.5.1), not sure if that is intentional or it should be updated.

I think I fixed it now by adding nvim-nio, upgrading to v0.9.1, and symlinking neotest into ~/.local/share/nvim/site/pack/vendor/start/neotest but now the last step is failing with a 403. Might be some permissions in the neotest repo that need to be updated or it might not be able to run in PRs but on the main repo.

[rcarriga]

Thank you for the new feature and also for giving the CI some love, I'll try find time to figure it out 😅 In the meantime though, this looks great!