**Description**

function test_cycle will be collected by pytest if this function is imported in a user-defined test.
Such an error will be emitted as pytest will treat it as a test.
```
test setup failed
file /opt/conda/lib/python3.8/site-packages/airflow/utils/dag_cycle_tester.py, line 27
  def test_cycle(dag):
E       fixture 'dag' not found
>       available fixtures: cache, capfd, capfdbinary, caplog, capsys, capsysbinary, doctest_namespace, monkeypatch, pytestconfig, record_property, record_testsuite_property, record_xml_attribute, recwarn, tmp_path, tmp_path_factory, tmpdir, tmpdir_factory
>       use 'pytest --fixtures [testpath]' for help on them.

```

**Use case / motivation**
This can be simply "fixed" by renaming this function to check_cycle although the user can do it upon importing this function.
This change by airflow will reduce the amount of surprise received by the end-user, and save a large number of debugging hours. 

**Are you willing to submit a PR?**
The changeset is too small to worth the trouble for a PR. 
airflow/models/dagbag.py
self.log.debug('Loaded DAG %s', dag)
        except (AirflowDagCycleException, AirflowDagDuplicatedIdException):
            
            self.log.exception('Exception bagging dag: %s', dag.dag_id)
            
            
            if recursive:
                for subdag in subdags:
                    if subdag.dag_id in self.dags:
                        del self.dags[subdag.dag_id]
            raise
    def collect_dags(
        self,
        dag_folder: Union[str, "pathlib.Path", None] = None,
        only_if_updated: bool = True,
        include_examples: bool = conf.getboolean('core', 'LOAD_EXAMPLES'),
        include_smart_sensor: bool = conf.getboolean('smart_sensor', 'USE_SMART_SENSOR'),
        safe_mode: bool = conf.getboolean('core', 'DAG_DISCOVERY_SAFE_MODE'),
    ):
        """
        Given a file path or a folder, this method looks for python modules,
        imports them and adds them to the dagbag collection.
        Note that if a ``.airflowignore`` file is found while processing
        the directory, it will behave much like a ``.gitignore``,
        ignoring files that match any of the regex patterns specified
        in the file.
        **Note**: The patterns in .airflowignore are treated as
        un-anchored regexes, not shell-like glob patterns.
        """
        if self.read_dags_from_db: