chore: bump actions/checkout to v7.0.0

[stefanamaerz]

Summary

Updated GitHub Actions checkout action to v7.0.0 across all workflows (ci.yml and release.yml) for security and maintenance improvements.

• Updated from actions/checkout@v6.0.2 to actions/checkout@v7.0.0
• Updated hash: 9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0
• All 3 occurrences in ci.yml and release.yml workflows updated

Test plan

• Verify workflows run successfully with the new action version
• Check that CI/CD processes continue to work as expected
• Confirm release workflow handles full git history properly

[stefanamaerz]

apologies for the noise here; my AI agent found the wrong bumblebee repo and opened this. If you want to merge it feel free, but I'll go ahead and close this out.