skip using a builder if not needed

Author: bpintea

x-pack/plugin/esql-core/src/main/java/org/elasticsearch/xpack/esql/core/expression/AttributeMap.java

@@ -386,9 +386,9 @@ public String toString() {
     }
 
     public static <E> AttributeMap<E> of(Attribute key, E value) {
-        var builder = new Builder<E>();
-        builder.put(key, value);
-        return builder.build();
+        final AttributeMap<E> map = new AttributeMap<>();
+        map.add(key, value);
+        return map;
     }
 
     public static <E> Builder<E> builder() {