Zola doesn't load .txt files as templates in Tera

[ky-bean]

Bug Report

Environment

Zola version: 0.19.2

Expected Behavior

Zola should allow .txt files to be loaded as available templates.

Current Behavior

Running zola build yields:

Building site...
Checking all internal links with anchors.
> Successfully checked 0 internal link(s) with anchors.
-> Creating 2 pages (0 orphan) and 2 sections
Error: Failed to serve the site
Error: Failed to render 'robots.txt'
Error: Reason: Template '[other.txt]' not found

Step to reproduce

• Create a zola site
• Add a file to the templates/ folder that ends in .txt, e.g. other.txt
• In another template, try to include the .txt file in the template, e.g. {% include "other.txt" %}
• Attempt to build the site with zola build or similar

Background

I was looking to add some functionality to my site in the form of utilizing a blocklist to extend my robots.txt. I tried simply extending the default robots.txt with an include but it failed as above. In looking for prior art regarding my use-case I came across this forum post describing the same issue. The discussion concluded with @Keats suggestion that adding txt to the file formats loaded by Tera should be fine.