[Feature] Support "Interval" function for dbt Models and Unit Testing

### Is this a new bug in dbt-redshift?

- [X] I believe this is a new bug in dbt-redshift
- [X] I have searched the existing issues, and I could not find an existing issue for this bug

### Current Behavior

I am running a dbt test on a working model and get a database error.
I can work around it by using dateadd instead of interval, but it is inconvenient.

### Expected Behavior

The unit test runs without database errors.

### Steps To Reproduce

Set up the unit test and the model and run `dbt test --select integration_metrics,test_type:unit`

integration_metrics_unit_test.yml:

version: 2

unit_tests:
- name: integration_metrics
description: "Test the aggregation of sent contracts for each integration and account."
model: integration_metrics
given:
- input: ref('account_usage')
rows:
- {account_id: 1, extension_id: 101, type: 'agreement_publish', created_time: '2024-09-15', position_id: 1001, collection_id: 2001}
- input: ref('extension_definition')
rows:
- {key: 'salesforce', category: 'sales_and_crm'}
expect:
rows:
- {workspaces_contracts_sent_last_3_months: 2}

integration_metrics.sql:

with
account_usage as (select * from {{ ref('account_usage') }}),

usage as (
select
extension_id,
count(
distinct case
when created_time between current_date - interval '6 month'
and current_date - interval '3 month'
then 1
end
) as integration_user_count_last_3_to_6_months
from account_usage
group by
extension_id
),

workspace_usage as (
select
extension_id,
listagg(distinct collection_id, ', ') within group (
order by collection_id
) as workspace_ids
from account_usage
group by
extension_id
),

usage_total as (
select ws_usage.workspace_ids as workspaces_contracts_sent_last_3_months
from usage
left join workspace_usage as ws_usage on usage.extension_id = ws_usage.extension_id
)

select coalesce(workspaces_contracts_sent_last_3_months, '') as workspaces_contracts_sent_last_3_months
from usage_total

### Relevant log output

```shell
dbt test --select integration_metrics,test_type:unit
06:10:50 Running with dbt=1.9.0-b2
06:10:50 Registered adapter: redshift=1.8.1
06:10:51 Found 185 models, 638 data tests, 3 seeds, 147 sources, 14 exposures, 674 macros, 2 unit tests
06:10:51
06:10:51 Concurrency: 1 threads (target='default_target')
06:10:51
06:11:05 1 of 1 START unit_test integration_metrics::integration_metrics ........................................................ [RUN]
...dbt-gi1dhiau/lib/python3.11/site-packages/dbt/adapters/sql/connections.py:93: UserWarning: DB-API extension cursor.connection used
cursor.execute(sql, bindings)
06:11:06 1 of 1 ERROR integration_metrics::integration_metrics .................................................................. [ERROR in 1.16s]
06:11:06
06:11:06 Finished running 1 unit test in 0 hours 0 minutes and 15.36 seconds (15.36s).
06:11:07
06:11:07 Completed with 1 error, 0 partial successs, and 0 warnings:
06:11:07
06:11:07 Runtime Error in unit_test integration_metrics (models/marts/standard/integration/integration_metrics_unit_tests.yml)
An error occurred during execution of unit test 'integration_metrics'. There may be an error in the unit test definition: check the data types.
Database Error
Interval values with month or year parts are not supported
06:11:07
06:11:07 Done. PASS=0 WARN=0 ERROR=1 SKIP=0 TOTAL=1
```

### Environment

```markdown
- OS:MacOS
- Python:3.9
- dbt-core:1.9.0
- dbt-redshift:1.8.1
```

### Additional Context

Note that I broke down the example as much as I could.
It's not as simple as running a select on account usage which was very frustrating :D
I mentioned the bug in the dbt channel but didn't get any feedback yet (For reference so I can update the thread once the issue is resolve): https://getdbt.slack.com/archives/CBSQTAPLG/p1728993577116609