2.9

Release notes: https://mcd-wiki.web.cern.ch/software/release_note/

What's Changed (automatically generated)

• Make key4hep image compatible with apptainer by @kkrizka in #7
• Update build instructions based on the v2.9 release series by @kkrizka in #10
• Hard code pushing to GHCR by @kkrizka in #11
• Adding self-hosted runner by @madbaron in #12
• Adding workflow dispatch by @madbaron in #13
• Lowercase owner name by @madbaron in #14

Full Changelog: 1.7...2.9