Fix CI badge to properly reflect main branch status

[Nick1200000]

Summary

Fixes the CI badge URL to properly display the status of the main branch only, resolving the issue introduced in #465.

Changes

• Updated the CI badge URL from /workflows/ci/badge.svg to /actions/workflows/ci.yml/badge.svg
• This uses the correct GitHub Actions badge format that properly supports branch-specific status

Problem Solved

• The previous badge URL format didn't reliably show main branch status
• Badge now consistently reflects CI status of the main branch, not random PR branches
• Prevents misleading "failing" status when experimental PRs have failing CI

Testing

• Verified the new badge URL displays correctly
• Badge shows current main branch CI status (passing)

Closes #474

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📚 Documentation preview 📚: https://causalpy--476.org.readthedocs.build/en/476/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.67%. Comparing base (89f369f) to head (2b8c05d).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #476   +/-   ##
=======================================
  Coverage   94.67%   94.67%           
=======================================
  Files          32       32           
  Lines        2196     2196           
=======================================
  Hits         2079     2079           
  Misses        117      117           

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[Nick1200000]

Hi @drbenvincent , please merge it, Thank you!

[drbenvincent]

Thanks @Nick1200000 :)

[Nick1200000]

@drbenvincent , if you need any support for Devops feel free to reach out to me

[drbenvincent]

Changed PR label to make the release notes for 0.4.2 more coherent