[BQ] Fix rendering for int64-type partition

[jtcohen6]

partition_by.render() was updated in v0.19.0 to handle granularity-based partitioning (week, month, year). This resulted in an regression for int64-type columns with incremental models using the insert_overwrite strategy.

https://github.com/fishtown-analytics/dbt/blob/6c6649f9129d5d108aa3b0526f634cd8f3a9d1ed/plugins/bigquery/dbt/adapters/bigquery/impl.py#L61-L65

Lines 61-62 should become:

 if self.data_type.lower() == 'int64' or (
         self.data_type.lower() == 'date' and
         self.granularity.lower() == 'day'
 ): 

Let's fix these lines and add:

• Unit tests for partition_by.render(). We added test_parse_partition_by in v0.16.0 for parsing old partition_by configs as new dict-style configs.
• An integration test case (022_bigquery_test): int64 + insert_overwrite

Steps to reproduce

{{ config(
    materialized = 'incremental',
    incremental_strategy = 'insert_overwrite',
    partition_by = {
        'field': 'id',
        'data_type': 'int64',
        'range': {
            'start': 0,
            'end': 10,
            'interval': 1
        }
    }
) }}

select 1 as id

$ dbt run
$ dbt run
...

Database Error in model int_table (models/int_table.sql)
  Query error: Function not found: int64_trunc at [33:34]
  compiled SQL at target/run/root_project/models/int_table.sql

v0.19.0:

when not matched by source
         and int64_trunc(DBT_INTERNAL_DEST.id, day) in unnest(dbt_partitions_for_replacement) 
        then delete

v0.18.1:

when not matched by source
         and DBT_INTERNAL_DEST.id in unnest(dbt_partitions_for_replacement) 
        then delete

Screenshots and log output

If applicable, add screenshots or log output to help explain your problem.

System information

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• snowflake
• other (specify: ____________)

The output of dbt --version:

$ dbt --version
installed version: 0.19.0
   latest version: 0.19.0

Up to date!

Plugins:
  - bigquery: 0.19.0
  - snowflake: 0.19.0
  - redshift: 0.19.0
  - postgres: 0.19.0