flatpak-builder: Add the git commit as the ostree commit subject

Author: alatiera

flatpak-builder/index.js

@@ -263,6 +263,7 @@ const build = async (manifest, manifestPath, cacheHitKey, config) => {
       config.bundle,
       `--runtime-repo=${config.repositoryUrl}`,
       `--arch=${config.arch}`,
+      `--subject=${github.context.sha}`,
       appId,
       branch
     ]