mbstring: Avoid pointless refcounted copy (php#20325)

These scalars can use the ZVAL_COPY_VALUE variant instead of ZVAL_COPY
because they don't need refcounting.

Author: ndossche

ext/mbstring/mbstring.c

@@ -2788,7 +2788,7 @@ MBSTRING_API HashTable *php_mb_convert_encoding_recursive(HashTable *input, cons
 			case IS_FALSE:
 			case IS_LONG:
 			case IS_DOUBLE:
-				ZVAL_COPY(&entry_tmp, entry);
+				ZVAL_COPY_VALUE(&entry_tmp, entry);
 				break;
 			case IS_ARRAY:
 				chash = php_mb_convert_encoding_recursive(