Silent failure when .netrc contains comments

[calebzulawski]

Checklist

• I added a descriptive title
• I searched open reports and couldn't find a duplicate

What happened?

When a .netrc file contains comments (leading #), the file is silently not used, leading to authentication errors. This was discovered with py-rattler but I believe it's actually due to the netrc-rs crate.

Additional Context

It doesn't appear netrc files actually support comments, though the curl and python implementations do support it. At a minimum, it would be nice if there were an error when parsing the netrc file fails (without an error, it appears to be a problem with the credentials).