Path collision report with a render = false section

[jplatte]

Bug Report

Environment

Zola version: 0.14.1

Expected Behavior

It should be possible to have both an index.md and _index.md if the latter has set render = false in its frontmatter.

Current Behavior

Failed to build the site
Error: Found path collisions:
- `/foo/` from files ["foo/_index.md", "foo/index.md"]

Step to reproduce

Sample repo: https://gitlab.com/flipdot/nusite/-/tree/broken
"Conflicting" files are found in content/projekte/3d-drucker/.