[fix](cast) fix wrong result while cast string to float (#31781)

Issue Number: close #31518

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/literal/FloatLiteral.java

@@ -46,6 +46,6 @@ public class FloatLiteral extends FractionalLiteral {
 
     @Override
     public LiteralExpr toLegacyLiteral() {
-        return new org.apache.doris.analysis.FloatLiteral((double) value, Type.FLOAT);
+        return new org.apache.doris.analysis.FloatLiteral(getDouble(), Type.FLOAT);
     }
 }