Fix migrate release from github (#19510)

* Fix migrate release from github

* Fix bug

services/migrations/gitea_uploader.go

@@ -7,6 +7,7 @@ package migrations
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -253,7 +254,6 @@ func (g *GiteaLocalUploader) CreateReleases(releases ...*base.Release) error {
 			LowerTagName: strings.ToLower(release.TagName),
 			Target:       release.TargetCommitish,
 			Title:        release.Name,
-			Sha1:         release.TargetCommitish,
 			Note:         release.Body,
 			IsDraft:      release.Draft,
 			IsPrerelease: release.Prerelease,
@@ -265,17 +265,20 @@ func (g *GiteaLocalUploader) CreateReleases(releases ...*base.Release) error {
 			return err
 		}
 
-		// calc NumCommits if no draft
-		if !release.Draft {
+		// calc NumCommits if possible
+		if rel.TagName != "" {
 			commit, err := g.gitRepo.GetTagCommit(rel.TagName)
+			if !errors.Is(err, git.ErrNotExist{}) {
 				if err != nil {
 					return fmt.Errorf("GetTagCommit[%v]: %v", rel.TagName, err)
 				}
+				rel.Sha1 = commit.ID.String()
 				rel.NumCommits, err = commit.CommitsCount()
 				if err != nil {
 					return fmt.Errorf("CommitsCount: %v", err)
 				}
 			}
+		}
 
 		for _, asset := range release.Assets {
 			if asset.Created.IsZero() {