Fixing TypeError: 'ExtractJob' object is not subscriptable

[lihan]

Traceback

Traceback (most recent call last):
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/providers/google/cloud/transfers/bigquery_to_gcs.py", line 128, in execute
    conf = job["configuration"]["extract"]["sourceTable"]
TypeError: 'ExtractJob' object is not subscriptable

The job is an ExtractJob object and cannot read its source table using subscript. So the code fixes it using object properties.

Since BigQueryTableLink is optional, using if to check it indeed returns an ExtractJob (part of BigQueryJob Union type).

[potiuk]

Yep. Some fixes needed @lihan :)

[potiuk]

Ci is telling what to fix

[potiuk]

Superseded by #24416