Add GitHub sponsorship

[martincostello]

Add GitHub logo from sponsorship and link to GitHub Secure Open Source Fund blog post.

[Copilot]

Pull Request Overview

This PR adds GitHub as a sponsor to the project by including their logo and a reference to their Secure Open Source Fund. It updates both the main README documentation and the community resources page to acknowledge GitHub's sponsorship.

• Adds GitHub's Secure Open Source Fund to the sponsors list in README.md
• Includes GitHub logo alongside existing sponsor logos
• Adds a blog post reference about GitHub's secure supply chain initiative to the community resources

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
README.md	Adds GitHub to sponsors section with logo and fund link
docs/community/resources.md	Adds reference to GitHub's secure supply chain blog post

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.23%. Comparing base (10be2ed) to head (bb90224).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2695   +/-   ##
=======================================
  Coverage   96.23%   96.23%           
=======================================
  Files         311      311           
  Lines        7322     7322           
  Branches     1012     1012           
=======================================
  Hits         7046     7046           
  Misses        222      222           
  Partials       54       54           

Flag	Coverage Δ
linux	96.23% <ø> (ø)
macos	96.23% <ø> (ø)
windows	96.22% <ø> (ø)

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