[Bug] `bigquery_use_batch_source_freshness` does not work

### Is this a new bug?

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

### Which packages are affected?

- [x] dbt-adapters
- [ ] dbt-tests-adapter
- [ ] dbt-athena
- [ ] dbt-athena-community
- [x] dbt-bigquery
- [ ] dbt-postgres
- [ ] dbt-redshift
- [ ] dbt-snowflake
- [ ] dbt-spark

### Current Behavior

Batch source freshness checking on BQ does not work as documented and errors.

### Expected Behavior

No errors.

### Steps To Reproduce

1. Create some sources:

```sql
create or replace table dbt_jyeo.customers as (
select 1 id, 'alice' as first_name, current_timestamp() as updated_at
);

create or replace table dbt_jyeo.orders as (
select 1 id, 100 as order_count, current_timestamp() as updated_at
);
```

2. Setup dbt project:

```yaml
# dbt_project.yml
name: dbt_basic_5
profile: all
version: "1.0.0"

models:
dbt_basic_5:
+materialized: table

flags:
bigquery_use_batch_source_freshness: True

# models/sources.yml
sources:
- name: dbt_jyeo
config:
freshness:
error_after: { count: 12, period: hour }
loaded_at_field: updated_at
tables:
- name: customers
- name: orders
```

3. Run source freshness checking:

```sh
$ dbt --debug source freshness

20:41:34 Sending event: {'category': 'dbt', 'action': 'invocation', 'label': 'start', 'context': [, , ]}
20:41:34 Running with dbt=1.11.7
20:41:34 running dbt with arguments {'empty': 'None', 'invocation_command': 'dbt --debug source freshness', 'use_colors': 'True', 'log_path': '/Users/jeremy/git/dbt-basic/logs', 'profiles_dir': '/Users/jeremy/.dbt', 'write_json': 'True', 'target_path': 'None', 'printer_width': '80', 'use_experimental_parser': 'False', 'cache_selected_only': 'False', 'debug': 'True', 'partial_parse': 'True', 'static_parser': 'True', 'log_format': 'default', 'warn_error_options': 'WarnErrorOptionsV2(error=[], warn=[], silence=[])', 'warn_error': 'None', 'log_cache_events': 'False', 'quiet': 'False', 'indirect_selection': 'eager', 'fail_fast': 'False', 'version_check': 'True', 'no_print': 'None', 'send_anonymous_usage_stats': 'True', 'introspect': 'True'}
20:41:43 Sending event: {'category': 'dbt', 'action': 'project_id', 'label': '44d14259-eb87-4f26-9ac7-a7ad64e5ebd6', 'context': []}
20:41:43 Sending event: {'category': 'dbt', 'action': 'adapter_info', 'label': '44d14259-eb87-4f26-9ac7-a7ad64e5ebd6', 'context': []}
20:41:43 Registered adapter: bigquery=1.11.1
20:41:43 checksum: b80718358155fc17c3559352095564dd56ada1cc1a1c0ef2e62c857e71583775, vars: {}, profile: , target: , version: 1.11.7
20:41:43 Unable to do partial parsing because of a version mismatch
20:41:43 Sending event: {'category': 'dbt', 'action': 'partial_parser', 'label': '44d14259-eb87-4f26-9ac7-a7ad64e5ebd6', 'context': []}
20:41:44 Sending event: {'category': 'dbt', 'action': 'load_project', 'label': '44d14259-eb87-4f26-9ac7-a7ad64e5ebd6', 'context': []}
20:41:44 Wrote artifact WritableManifest to /Users/jeremy/git/dbt-basic/target/manifest.json
20:41:44 Wrote artifact SemanticManifest to /Users/jeremy/git/dbt-basic/target/semantic_manifest.json
20:41:44 Sending event: {'category': 'dbt', 'action': 'resource_counts', 'label': '44d14259-eb87-4f26-9ac7-a7ad64e5ebd6', 'context': []}
20:41:44 Found 2 models, 2 sources, 539 macros
20:41:44 Sending event: {'category': 'dbt', 'action': 'runnable_timing', 'label': '44d14259-eb87-4f26-9ac7-a7ad64e5ebd6', 'context': []}
20:41:44
20:41:44 Concurrency: 4 threads (target='bq')
20:41:44
20:41:44 Acquiring new bigquery connection 'master'
20:41:44 Acquiring new bigquery connection 'list_cse-sandbox-319708_dbt_jyeo'
20:41:44 Opening a new connection, currently in state init
20:41:44 Sending event: {'category': 'dbt', 'action': 'runnable_timing', 'label': '44d14259-eb87-4f26-9ac7-a7ad64e5ebd6', 'context': []}
20:41:44 Opening a new connection, currently in state init
20:41:44 Pulling freshness from warehouse metadata tables for 0 sources
20:41:44 BigQuery adapter: Unhandled error while running:
macro get_relation_last_modified
20:41:44 BigQuery adapter: Compilation Error
list object has no element 0

> in macro get_relation_last_modified (macros/adapters/metadata.sql)
> called by
20:41:44 Metadata freshness could not be computed in batch: Compilation Error
list object has no element 0

> in macro get_relation_last_modified (macros/adapters/metadata.sql)
> called by
20:41:44 Began running node source.dbt_basic_5.dbt_jyeo.customers
20:41:44 Began running node source.dbt_basic_5.dbt_jyeo.orders
20:41:44 1 of 2 START freshness of dbt_jyeo.customers ................................... [RUN]
20:41:44 2 of 2 START freshness of dbt_jyeo.orders ...................................... [RUN]
20:41:44 Re-using an available connection from the pool (formerly list_cse-sandbox-319708_dbt_jyeo, now source.dbt_basic_5.dbt_jyeo.customers)
20:41:44 Acquiring new bigquery connection 'source.dbt_basic_5.dbt_jyeo.orders'
20:41:44 Began compiling node source.dbt_basic_5.dbt_jyeo.customers
20:41:44 Began compiling node source.dbt_basic_5.dbt_jyeo.orders
20:41:44 Began executing node source.dbt_basic_5.dbt_jyeo.customers
20:41:44 Began executing node source.dbt_basic_5.dbt_jyeo.orders
20:41:44 On source.dbt_basic_5.dbt_jyeo.customers: /* {"app": "dbt", "dbt_version": "1.11.7", "profile_name": "all", "target_name": "bq", "node_id": "source.dbt_basic_5.dbt_jyeo.customers"} */
select
max(updated_at) as max_loaded_at,
current_timestamp() as snapshotted_at
from `cse-sandbox-319708`.`dbt_jyeo`.`customers`


20:41:44 On source.dbt_basic_5.dbt_jyeo.orders: /* {"app": "dbt", "dbt_version": "1.11.7", "profile_name": "all", "target_name": "bq", "node_id": "source.dbt_basic_5.dbt_jyeo.orders"} */
select
max(updated_at) as max_loaded_at,
current_timestamp() as snapshotted_at
from `cse-sandbox-319708`.`dbt_jyeo`.`orders`


20:41:44 Opening a new connection, currently in state closed
20:41:44 Opening a new connection, currently in state init
20:41:45 BigQuery adapter: https://console.cloud.google.com/bigquery?project=cse-sandbox-319708&j=bq:US:48964da4-cde3-4533-8c9a-40182a3c7c0c&page=queryresults
20:41:45 BigQuery adapter: https://console.cloud.google.com/bigquery?project=cse-sandbox-319708&j=bq:US:d1988066-72aa-462c-a4e7-bba0ff58ff36&page=queryresults
20:41:46 SQL status: OK in 0.401 seconds
20:41:46 1 of 2 PASS freshness of dbt_jyeo.customers .................................... [PASS in 1.97s]
20:41:46 Finished running node source.dbt_basic_5.dbt_jyeo.customers
20:41:47 SQL status: OK in 1.423 seconds
20:41:47 2 of 2 PASS freshness of dbt_jyeo.orders ....................................... [PASS in 2.96s]
20:41:47 Finished running node source.dbt_basic_5.dbt_jyeo.orders
20:41:47 Connection 'master' was properly closed.
20:41:47 Connection 'source.dbt_basic_5.dbt_jyeo.customers' was properly closed.
20:41:47 Connection 'source.dbt_basic_5.dbt_jyeo.orders' was properly closed.
20:41:47
20:41:47 Finished running 2 sources in 0 hours 0 minutes and 3.66 seconds (3.66s).
20:41:47 Wrote artifact WritableManifest to /Users/jeremy/git/dbt-basic/target/manifest.json
20:41:47 Wrote artifact SemanticManifest to /Users/jeremy/git/dbt-basic/target/semantic_manifest.json
20:41:47 Wrote artifact FreshnessResult to /Users/jeremy/git/dbt-basic/target/sources.json
20:41:47 Done.
20:41:47 Resource report: {"command_name": "freshness", "command_success": true, "command_wall_clock_time": 13.1265545, "process_in_blocks": "0", "process_kernel_time": 0.550304, "process_mem_max_rss": "250527744", "process_out_blocks": "0", "process_user_time": 2.694914}
20:41:47 Command `dbt source freshness` succeeded at 13:41:47.844146 after 13.13 seconds
20:41:47 Sending event: {'category': 'dbt', 'action': 'invocation', 'label': 'end', 'context': [, , ]}
20:41:47 Flushing usage events
20:41:48 An error was encountered while trying to flush usage events
```

### Relevant log output

```shell

```

### Environment

```markdown
- OS: macOS
- Python: 3.11.9
- dbt-adapters: 1.22.9
- dbt-bigquery: 1.11.7
```

### Additional Context

I overrode the `bigquery__get_relation_last_modified` macro and printed `relations` at the start of the macro and it was empty at the time which is likely the cause for:

```
list object has no element 0
```