Fix misspelling of mergable (#30896)

https://github.com/go-gitea/gitea/pull/25812#issuecomment-2099833692
Follow #30573

routers/web/repo/pull.go

@@ -1007,7 +1007,7 @@ func MergePullRequest(ctx *context.Context) {
 	}
 
 	// start with merging by checking
-	if err := pull_service.CheckPullMergable(ctx, ctx.Doer, &ctx.Repo.Permission, pr, mergeCheckType, form.ForceMerge); err != nil {
+	if err := pull_service.CheckPullMergeable(ctx, ctx.Doer, &ctx.Repo.Permission, pr, mergeCheckType, form.ForceMerge); err != nil {
 		switch {
 		case errors.Is(err, pull_service.ErrIsClosed):
 			if issue.IsPull {
@@ -1021,7 +1021,7 @@ func MergePullRequest(ctx *context.Context) {
 			ctx.JSONError(ctx.Tr("repo.pulls.has_merged"))
 		case errors.Is(err, pull_service.ErrIsWorkInProgress):
 			ctx.JSONError(ctx.Tr("repo.pulls.no_merge_wip"))
-		case errors.Is(err, pull_service.ErrNotMergableState):
+		case errors.Is(err, pull_service.ErrNotMergeableState):
 			ctx.JSONError(ctx.Tr("repo.pulls.no_merge_not_ready"))
 		case models.IsErrDisallowedToMerge(err):
 			ctx.JSONError(ctx.Tr("repo.pulls.no_merge_not_ready"))