**Apache Airflow version**: 2.0.0a1
**What happened**:

When a task fails on the first try, the log output for additional tries go to the log for the first attempt.

**What you expected to happen**:

The logs should go to the correct log file. For the default configuration, the log filename template is `log_filename_template = {{ ti.dag_id }}/{{ ti.task_id }}/{{ ts }}/{{ try_number }}.log`, so additional numbered `.log` files should be created.

**How to reproduce it**:

Create a test dag:

```
from datetime import timedelta
from airflow import DAG
from airflow.operators.python import PythonOperator
from airflow.utils.dates import days_ago


with DAG(
    dag_id="trynumber_demo",
    default_args={"start_date": days_ago(2), "retries": 1, "retry_delay": timedelta(0)},
    schedule_interval=None,
) as dag:

    def demo_task(ti=None):
        print("Running demo_task, try_number =", ti.try_number)
        if ti.try_number <= 1:
            raise ValueError("Shan't")

    task = PythonOperator(task_id="demo_task", python_callable=demo_task)
```

and trigger this dag:

```
$ airflow dags trigger trynumber_demo
```

then observe that `triggernumber_demo/demo_task/<execution_date>/` only contains 1.log, which contains the full output for 2 runs:

```
[...]
--------------------------------------------------------------------------------
[2020-10-21 13:29:07,958] {taskinstance.py:1020} INFO - Starting attempt 1 of 2
[2020-10-21 13:29:07,959] {taskinstance.py:1021} INFO -
--------------------------------------------------------------------------------
[...]
[2020-10-21 13:29:08,163] {logging_mixin.py:110} INFO - Running demo_task, try_number = 1
[2020-10-21 13:29:08,164] {taskinstance.py:1348} ERROR - Shan't
Traceback (most recent call last):
[...]
ValueError: Shan't
[2020-10-21 13:29:08,168] {taskinstance.py:1392} INFO - Marking task as UP_FOR_RETRY. dag_id=trynumber_demo, task_id=demo_task, execution_date=20201021T122907, start_date=20201021T122907, end_date=20201021T122908
[...]
[2020-10-21 13:29:09,121] {taskinstance.py:1019} INFO -
--------------------------------------------------------------------------------
[2020-10-21 13:29:09,121] {taskinstance.py:1020} INFO - Starting attempt 2 of 2
[2020-10-21 13:29:09,121] {taskinstance.py:1021} INFO -
--------------------------------------------------------------------------------
[...]
[2020-10-21 13:29:09,333] {logging_mixin.py:110} INFO - Running demo_task, try_number = 2
[2020-10-21 13:29:09,334] {python.py:141} INFO - Done. Returned value was: None
[2020-10-21 13:29:09,355] {taskinstance.py:1143} INFO - Marking task as SUCCESS.dag_id=trynumber_demo, task_id=demo_task, execution_date=20201021T122907, start_date=20201021T122909, end_date=20201021T122909
[2020-10-21 13:29:09,404] {local_task_job.py:117} INFO - Task exited with return code 0
```

The `TaskInstance()` created for the run needs to first be refreshed from the database, before setting the logging context.
tests/cli/commands/test_task_command.py
with conf_vars({('core', 'dags_folder'): os.path.join(ROOT_FOLDER, f"tests/dags/{self.dag_id}")}):
            task_command.task_run(self.parser.parse_args([
                'tasks', 'run', self.dag_id, self.task_id, '--local', self.execution_date_str]))
        with open(self.ti_log_file_path) as l_file:
            logs = l_file.read()
        print(logs)     
        logs_list = logs.splitlines()
        self.assertIn(f"Subtask {self.task_id}", logs)
        self.assertIn("base_task_runner.py", logs)
        self.assert_log_line("Log from DAG Logger", logs_list)
        self.assert_log_line("Log from TI Logger", logs_list)
        self.assert_log_line("Log from Print statement", logs_list, expect_from_logging_mixin=True)
        self.assertIn(f"INFO - Running: ['airflow', 'tasks', 'run', '{self.dag_id}', "
                      f"'{self.task_id}', '{self.execution_date_str}',", logs)
        self.assertIn(f"INFO - Marking task as SUCCESS.dag_id={self.dag_id}, "
                      f"task_id={self.task_id}, execution_date=20170101T000000", logs)
class TestCliTaskBackfill(unittest.TestCase):