Mark TemplateLoading error as "UnprocessableEntity" (#19445)

- Don't return Internal Server error if the user provide incorrect label
template, instead return UnprocessableEntity.
- Resolves #19399

routers/api/v1/repo/repo.go

@@ -22,6 +22,7 @@ import (
 	"code.gitea.io/gitea/modules/convert"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
+	repo_module "code.gitea.io/gitea/modules/repository"
 	"code.gitea.io/gitea/modules/setting"
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/util"
@@ -248,7 +249,8 @@ func CreateUserRepo(ctx *context.APIContext, owner *user_model.User, opt api.Cre
 		if repo_model.IsErrRepoAlreadyExist(err) {
 			ctx.Error(http.StatusConflict, "", "The repository with the same name already exists.")
 		} else if db.IsErrNameReserved(err) ||
-			db.IsErrNamePatternNotAllowed(err) {
+			db.IsErrNamePatternNotAllowed(err) ||
+			repo_module.IsErrIssueLabelTemplateLoad(err) {
 			ctx.Error(http.StatusUnprocessableEntity, "", err)
 		} else {
 			ctx.Error(http.StatusInternalServerError, "CreateRepository", err)