iceberg: detect table-exists through the wrapped manager error (#10075)

handleCreateTable used a type assertion that fails through WithFilerClient's
'all filers failed' wrap, so a concurrent create that the pre-check missed
fell through instead of returning the existing table. Use errors.As.

weed/s3api/iceberg/handlers_table.go

@@ -263,7 +263,8 @@ func (s *Server) handleCreateTable(w http.ResponseWriter, r *http.Request) {
 	})
 
 	if err != nil {
-		if tableErr, ok := err.(*s3tables.S3TablesError); ok && tableErr.Type == s3tables.ErrCodeTableAlreadyExists {
+		var tableErr *s3tables.S3TablesError
+		if errors.As(err, &tableErr) && tableErr.Type == s3tables.ErrCodeTableAlreadyExists {
 			getReq := &s3tables.GetTableRequest{
 				TableBucketARN: bucketARN,
 				Namespace:      namespace,