**Apache Airflow version**: 2.1.0

**What happened**:
Airflow logging assume dict_key is type `str`
```
    logging.info("Dictionary where key is int type: %s", modified_table_mapping)
  File "/usr/lib64/python3.6/logging/__init__.py", line 1902, in info
    root.info(msg, *args, **kwargs)
  File "/usr/lib64/python3.6/logging/__init__.py", line 1308, in info
    self._log(INFO, msg, args, **kwargs)
  File "/usr/lib64/python3.6/logging/__init__.py", line 1444, in _log
    self.handle(record)
  File "/usr/lib64/python3.6/logging/__init__.py", line 1453, in handle
    if (not self.disabled) and self.filter(record):
  File "/usr/lib64/python3.6/logging/__init__.py", line 720, in filter
    result = f.filter(record)
  File "/bb/bin/airflow_env/lib/python3.6/site-packages/airflow/utils/log/secrets_masker.py", line 157, in filter
    record.__dict__[k] = self.redact(v)
  File "/bb/bin/airflow_env/lib/python3.6/site-packages/airflow/utils/log/secrets_masker.py", line 193, in redact
    return {dict_key: self.redact(subval, dict_key) for dict_key, subval in item.items()}
  File "/bb/bin/airflow_env/lib/python3.6/site-packages/airflow/utils/log/secrets_masker.py", line 193, in <dictcomp>
    return {dict_key: self.redact(subval, dict_key) for dict_key, subval in item.items()}
  File "/bb/bin/airflow_env/lib/python3.6/site-packages/airflow/utils/log/secrets_masker.py", line 189, in redact
    if name and should_hide_value_for_key(name):
  File "/bb/bin/airflow_env/lib/python3.6/site-packages/airflow/utils/log/secrets_masker.py", line 74, in should_hide_value_for_key
    name = name.strip().lower()
AttributeError: 'int' object has no attribute 'strip'
```

**How to reproduce it**:
Define a dictionary where the type of keys is `int` and print it in any Airflow tasks.

tests/utils/log/test_secrets_masker.py
"""
        Test that when ``logger.exception`` is called when there is no current exception we still log.
        (This is a "bug" in user code, but we shouldn't die because of it!)
        """
        logger.exception("Err")
        assert caplog.text == textwrap.dedent(
            """\
            ERROR Err
            NoneType: None
            """
        )
    @pytest.mark.xfail(reason="Cannot filter secrets in traceback source")
    def test_exc_tb(self, logger, caplog):
        """
        Show it is not possible to filter secrets in the source.
        It is not possible to (regularly/reliably) filter out secrets that
        appear directly in the source code. This is because the formatting of
        exc_info is not done in the filter, it is done after the filter is
        called, and fixing this "properly" is hard/impossible.
        (It would likely need to construct a custom traceback that changed the
        source. I have no idead if that is even possible)
        This test illustrates that, but ix marked xfail in case someone wants to
        fix this later.
        """