**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
return
        self.log.info("Filling up the DagBag from %s", dag_folder)
        dag_folder = dag_folder or self.dag_folder
        
        stats = []
        
        dag_folder = correct_maybe_zipped(str(dag_folder))
        for filepath in list_py_file_paths(
            dag_folder,
            safe_mode=safe_mode,
            include_examples=include_examples,
            include_smart_sensor=include_smart_sensor,
        ):
            try:
                file_parse_start_dttm = timezone.utcnow()
                found_dags = self.process_file(filepath, only_if_updated=only_if_updated, safe_mode=safe_mode)
                file_parse_end_dttm = timezone.utcnow()
                stats.append(
                    FileLoadStat(
                        file=filepath.replace(settings.DAGS_FOLDER, ''),
                        duration=file_parse_end_dttm - file_parse_start_dttm,
                        dag_num=len(found_dags),
                        task_num=sum(len(dag.tasks) for dag in found_dags),
                        dags=str([dag.dag_id for dag in found_dags]),
                    )
                )
            except Exception as e:  
                self.log.exception(e)
        self.dagbag_stats = sorted(stats, key=lambda x: x.duration, reverse=True)
    def collect_dags_from_db(self):