**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.

airflow/utils/log/secrets_masker.py
"""
    Mask a secret from appearing in the task logs.
    If ``name`` is provided, then it will only be masked if the name matches
    one of the configured "sensitive" names.
    If ``secret`` is a dict or a iterable (excluding str) then it will be
    recursively walked and keys with sensitive names will be hidden.
    """
    
    from airflow import settings
    
    
    if not settings.MASK_SECRETS_IN_LOGS or not secret:
        return
    _secrets_masker().add_mask(secret, name)
def redact(value: "RedactableItem", name: str = None) -> "RedactableItem":
    """Redact any secrets found in ``value``."""
    return _secrets_masker().redact(value, name)
@cache
def _secrets_masker() -> "SecretsMasker":
    for flt in logging.getLogger('airflow.task').filters:
        if isinstance(flt, SecretsMasker):
            return flt
    raise RuntimeError("No SecretsMasker found!")
class SecretsMasker(logging.Filter):