### Apache Airflow version

main (development)

### What happened

1. When not providing `project_id` to `BigQueryGetDataOperator` in deferrable mode (`project_id=None`), the query generated by `generate_query` method is bugged, i.e.,: 

````sql
from `None.DATASET.TABLE_ID` limit ...
````

2. `as_dict` param does not work `BigQueryGetDataOperator`.

### What you think should happen instead

1. When `project_id` is `None` - it should be removed from the query along with the trailing dot, i.e.,:

````sql
from `DATASET.TABLE_ID` limit ...
````

2. `as_dict` should be added to the serialization method of `BigQueryGetDataTrigger`.

### How to reproduce

1. Create a DAG file with `BigQueryGetDataOperator` defined as follows:
```python
BigQueryGetDataOperator(
        task_id="bq_get_data_op",
        # project_id="PROJECT_ID",  <-- Not provided
        dataset_id="DATASET",
        table_id="TABLE",
        use_legacy_sql=False,
        deferrable=True
    )
````

2. 1. Create a DAG file with `BigQueryGetDataOperator` defined as follows:
```python
BigQueryGetDataOperator(
        task_id="bq_get_data_op",
        project_id="PROJECT_ID",
        dataset_id="DATASET",
        table_id="TABLE",
        use_legacy_sql=False,
        deferrable=True,
        as_dict=True
    )
````

### Operating System

Debian

### Versions of Apache Airflow Providers

_No response_

### Deployment

Official Apache Airflow Helm Chart

### Deployment details

_No response_

### Anything else

The `generate_query` method is not unit tested (which would have prevented it in the first place) - will be better to add one.

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

"mode": "REQUIRED",
                "name": "salary",
                "type": "INTEGER"
              }
            ]
        **Example (with schema in the DAG)**: ::
            CreateTable = BigQueryCreateEmptyTableOperator(
                task_id='BigQueryCreateEmptyTableOperator_task',
                dataset_id='ODS',
                table_id='Employees',
                project_id='internal-gcp-project',
                schema_fields=[{"name": "emp_name", "type": "STRING", "mode": "REQUIRED"},
                               {"name": "salary", "type": "INTEGER", "mode": "NULLABLE"}],
                gcp_conn_id='airflow-conn-id-account',
                google_cloud_storage_conn_id='airflow-conn-id'
            )
    :param view: [Optional] A dictionary containing definition for the view.
        If set, it will create a view instead of a table:
        .. seealso::
            https://cloud.google.com/bigquery/docs/reference/rest/v2/tables#ViewDefinition
    :param materialized_view: [Optional] The materialized view definition.
    :param encryption_configuration: [Optional] Custom encryption configuration (e.g., Cloud KMS keys).
        **Example**: ::
            encryption_configuration = {
                "kmsKeyName": "projects/testp/locations/us/keyRings/test-kr/cryptoKeys/test-key"
            }
    :param location: The location used for the operation.
    :param cluster_fields: [Optional] The fields used for clustering.
            BigQuery supports clustering for both partitioned and
            non-partitioned tables.