Support backing up a source file that is a symlink

What does this Merge Request do and why?

This MR fixes a bug where backing up a source file that's a symlink (common in a Gitpod instance) causes an exception.

Closes #1292 (closed)

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.