Fix operator precedence problem in Parquet reader (#15638)

Fixes an operator precedence problem with a bitwise `&` that was not detected because it was accidentally correct. `PAGEINFO_FLAGS_DICTIONARY` has a value of '1', so `PAGEINFO_FLAGS_DICTIONARY != 0` evaluates to '1', and that ANDed with the page flags evaluates `true` when the bit is set.

Authors:
  - Ed Seidl (https://github.com/etseidl)

Approvers:
  - Bradley Dice (https://github.com/bdice)
  - Vukasin Milovanovic (https://github.com/vuule)
  - Nghia Truong (https://github.com/ttnghia)

URL: #15638

cpp/src/io/parquet/page_decode.cuh

@@ -122,7 +122,7 @@ struct null_count_back_copier {
  */
 constexpr bool is_string_col(PageInfo const& page, device_span<ColumnChunkDesc const> chunks)
 {
-  if (page.flags & PAGEINFO_FLAGS_DICTIONARY != 0) { return false; }
+  if ((page.flags & PAGEINFO_FLAGS_DICTIONARY) != 0) { return false; }
   auto const& col = chunks[page.chunk_idx];
   return is_string_col(col);
 }