fix: support repositories with immutable releases enabled

GitHub's immutable releases feature (GA since Oct 2025) prevents
modifying release artifacts after the release is created. This broke
chart-releaser because it creates the release first, then uploads
assets in a separate API call.

This fix creates releases as drafts first, uploads assets, then
publishes the release. Draft releases can be modified until they
are published, which allows the asset upload to succeed.

Fixes helm/chart-releaser-action#228

See: https://github.blog/changelog/2025-10-28-immutable-releases-are-now-generally-available/
Signed-off-by: Chris Burr <christopher.burr@cern.ch>

Author: chrisburr

pkg/github/github.go

@@ -102,15 +102,22 @@ func (c *Client) GetRelease(_ context.Context, tag string) (*Release, error) {
 	return result, nil
 }
 
-// CreateRelease creates a new release object in the GitHub API
+// CreateRelease creates a new release object in the GitHub API.
+// To support repositories with immutable releases enabled (see
+// https://github.blog/changelog/2025-10-28-immutable-releases-are-now-generally-available/),
+// the release is first created as a draft, assets are uploaded, and then
+// the release is published. This ensures that assets can be uploaded before
+// the release becomes immutable.
 func (c *Client) CreateRelease(_ context.Context, input *Release) error {
+	draft := true
 	req := &github.RepositoryRelease{
 		Name:                 &input.Name,
 		Body:                 &input.Description,
 		TagName:              &input.Name,
 		TargetCommitish:      &input.Commit,
 		GenerateReleaseNotes: &input.GenerateReleaseNotes,
 		MakeLatest:           &input.MakeLatest,
+		Draft:                &draft,
 	}
 
 	release, _, err := c.Repositories.CreateRelease(context.TODO(), c.owner, c.repo, req)
@@ -123,6 +130,17 @@ func (c *Client) CreateRelease(_ context.Context, input *Release) error {
 			return err
 		}
 	}
+
+	// Publish the release by setting draft to false
+	draft = false
+	req = &github.RepositoryRelease{
+		Draft: &draft,
+	}
+	_, _, err = c.Repositories.EditRelease(context.TODO(), c.owner, c.repo, *release.ID, req)
+	if err != nil {
+		return errors.Wrap(err, "failed to publish release")
+	}
+
 	return nil
 }