Skip directories with insufficient permissions instead of exiting

[fpiribauer]

When tms encounters a directory it cannot read due to insufficient permissions, it will abort with

$ tms
Error: IO Error
├╴at src/repos.rs:58:18
├╴Could not read directory "/home/piri/a_test_directory"
│
╰─▶ Permission denied (os error 13)
    ╰╴at src/repos.rs:58:18

I'm one of these rebellious people that sometimes has directories in my home tree that my user cannot read (mostly docker related bind mounts). This change will make tms skip such directories and write a warning instead.

[jrmoulton]

Thanks!