1.6.1 - fix amnesia during multipe type mismatches

• 1.6.1 (2024-01-12)
  • Bug Fix: Prevent amnesia that causes multiple type mismatches warnings
    • If a data set contains multiple records with a column which do not
      match each other, then the old code would remove the corresponding
      internal schema_entry for that column, and print a warning message.
    • This means that subsequent records would recreate the schema_entry,
      and a subsequent mismatch would print another warning message.
    • This also meant that if there was a second record after the most
      recent mismatch, the script would output a schema entry for the
      mismatching column, corresponding to the type of the last record which
      was not marked as a mismatch.
    • The fix is to use a tombstone entry for the offending column, instead
      of deleting the schema_entry completely. Only a single warning
      message is printed, and the column is ignored for all subsequent
      records in the input data set.
    • See
      [Issue#98](https://github.com/bxparks/bigquery-schema-generator/issues/98]
      which identified this problem which seems to have existed from the
      very beginning.