Include_relative liquid tag inside collection doc doesnt work

[hosnas]

• I believe this to be a bug, not a question about using Jekyll.
• I updated to the latest Jekyll (or) if on GitHub Pages to the latest github-pages
• I ran jekyll doctor to check my configuration

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• I am on (or have tested on) Debian/Ubuntu GNU/Linux

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• I was trying to build.

My Reproduction Steps

I'm trying to use include_relative liquid tag inside one of my collections document but it is giving me an error:
Liquid Exception: Could not locate the included file
I found that it happens only when I put all my collections inside a collection_dir folder . when collection_dir is not defined, the problem doesn't occur.

I have also created this repository for reference:
https://github.com/hosnas/jekyll-test-1
the document is in collections/col1 folder named index.md and the included file is fa.md beside it.

The Output I Wanted

It should normally give me no error and include_relative liquid tag should work as expected.

[ashmaroli]

This seems like a legit bug to me.
I hadn't considered this at all when I refactored the collections_dir feature in #6685

Thank you @hosnas for reporting this and including a test-repo.