Dependency Upgrades

[ckenst]

Conference/Workshop Details

None

Checklist

• I have added the conference/workshop to the correct YAML file (_data/current.yml or _data/past.yml)
• The entry includes name, location, date(s), url and accurate status
• The entry is in chronological order (soonest to furtherest away)
• If there are any special characters in the name field (: or ; or '), the name must be in quotes (")
• I have checked for duplicates to avoid listing the same event twice
• Build runs successfully

Additional context

Lots of dependency upgrades. Should also probably move away from CircleCI and just use GitHub Actions.

[Copilot]

Pull Request Overview

This PR contains dependency upgrades and modernization updates to bring the project up to date with newer versions of Jekyll, Ruby, and related dependencies.

• Updated Jekyll from version 3.8.6 to 4.2.2 and Ruby from 2.6.10 to 3.1
• Modernized Docker Compose configuration by removing deprecated version specification
• Improved 404 error page layout and added new SETUP.md documentation

Reviewed Changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
docker-compose.yml	Updated Jekyll image version and removed deprecated version field
Gemfile	Upgraded Jekyll, github-pages versions and removed nokogiri dependency
.circleci/config.yml	Updated Ruby image and Bundler versions
404.html	Restructured page layout and updated Font Awesome references
SETUP.md	Added new local development setup documentation
subscribe.html	Updated last modified date and reformatted text
sponsorships.md	Updated last modified date

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