disable git fsck for mirrored repos by default (#6018)

models/repo.go

@@ -1379,7 +1379,7 @@ func CreateRepository(doer, u *User, opts CreateRepoOptions) (_ *Repository, err
 		LowerName:     strings.ToLower(opts.Name),
 		Description:   opts.Description,
 		IsPrivate:     opts.IsPrivate,
-		IsFsckEnabled: true,
+		IsFsckEnabled: !opts.IsMirror,
 	}
 
 	sess := x.NewSession()