main/chicken: update to 6.0.0

[j0ni]

Description

Update chicken scheme to version 6.0.0, a major release implementing the R7RS small language.

Checklist

Before this pull request is reviewed, certain conditions must be met.

The following must be true for all changes:

• I have read CONTRIBUTING.md
• I acknowledge that overtly not following the above or the below will result in my pull request getting closed
• I acknowledge https://gts.chimera-linux.org/@chimera/statuses/01KWARHE1BXBMXB8WPXK0BBM1B (temporary)

The following must be true for template/package changes:

• I have read Packaging.md
• I have built and tested my changes on my machine

[j0ni]

Thanks @z-erica for the pointers - I've made the suggested edits and squashed them per guidelines.