Fix MyPy issues in ``airflow/providers/amazon/aws/transfers`` (#20708)
Fix MyPy issues in ``airflow/providers/amazon/aws/transfers`` (#20708)

We were using ``cast`` redundantly.

Before:

```
root@de8d91a123ec:/opt/airflow# mypy --namespace-packages airflow/providers/amazon/aws/transfers
airflow/providers/amazon/aws/transfers/gcs_to_s3.py:185: error: Redundant cast to "bytes"
                        cast(bytes, file_bytes), key=dest_key, replace=self.replace, acl_policy=self.s3_acl_policy
                        ^
Found 1 error in 1 file (checked 18 source files)
```

After:
```
root@de8d91a123ec:/opt/airflow# mypy --namespace-packages airflow/providers/amazon/aws/transfers
Success: no issues found in 18 source files
```
lyft/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,lyft/incubator-airflow,bolkedebruin/airflow,apache/airflow,nathanielvarona/airflow,nathanielvarona/airflow,apache/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,bolkedebruin/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,apache/airflow,apache/airflow,bolkedebruin/airflow,apache/airflow,cfei18/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,mistercrunch/airflow