skip directories with perm error when building autoimport index

[MrBago]

Description

WIth this fix, rope will skip folders in sys.path that the user does not have permission to access instead of failing the entire cache build.

Fixes #(issue)

Checklist (delete if not relevant):

• [x] I have added tests that prove my fix is effective or that my feature works
• [ ] I have updated CHANGELOG.md
• [ ] I have made corresponding changes to user documentation for new features
• [ ] I have made corresponding changes to library documentation for API changes

[MrBago]

I ran into this minor issue when working on my other PR so here's a quick patch.

[tkrabel-db]

@MrBago thanks for that! LGTM.

[MrBago]

@lieryan Happy new year! When you have a min, can you look the update I made to this PR?

[lieryan]

Thanks for fixing this issue @MrBago

[lieryan]

@all-contributors add @MrBago for code contribution

[allcontributors[bot]]

@lieryan

I've put up a pull request to add @MrBago! :tada: