Enforce safe directory - #762

This pr fixes #760 by setting the repositories path as a safe directory when running checkout and removing that config on cleanup.

We aren't able to set it as a local config, as this setting only works for global configs.

So, using the standard we used for submodules, lets go ahead and copy the existing global config to a new location. Then we can go ahead and modify that global config (so we don't modify like a users global config if they test something on a self hosted runner real fast). Then, we can delete that global config at the end of the checkout step.

This does carry some limitations, it doesn't persist this configuration for the duration of the job mainly. So if your job pushes to git or something after checkout, that will continue to fail. We need to figure out how to address this at an ecosystem level, outside of the checkout action.