Update flatpak-builder to 1.2.1
Changes:
- Use the external debugedit project instead of using an internal copy
- New secret-opts feature lets you pass e.g. CI secrets into the build
- Support content-encoding when downloading
- New inline data source allowing easy creation of files from embedded content from the manifest
- Add missing newlines in some output
- Fix missing error check in the new inline data support
- Fix debuginfo being re-processed multiple times in a manifest
- Change manifest parsing issues from warnings to fatal errors
- Add .tar.zst archive support
- Fix auto-detection of .7z archives
- Install a JSON schema for manifest format