Unable to delete tags when syncing mirror

• Gitea version (or commit ref): 1.6.0-rc1 / aeb5655
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist:

[...odels/repo_mirror.go:335 SyncMirrors()] [E] Failed to synchronize tags to releases for repository: GetTagCommitID: object does not exist [id: refs/tags/test, rel_path: ]

Description

Step to reproduce:

1. Delete a tag from Repo1
2. Sync Repo2 (mirror of Repo1)

gitea/models/release.go

Lines 488 to 495 in aeb5655

	commitID, err := gitRepo.GetTagCommitID(rel.TagName)
	if err != nil {
	return fmt.Errorf("GetTagCommitID: %v", err)
	}
	if !gitRepo.IsTagExist(rel.TagName) || commitID != rel.Sha1 {
	if err := pushUpdateDeleteTag(repo, gitRepo, rel.TagName); err != nil {
	return fmt.Errorf("pushUpdateDeleteTag: %v", err)
	}