**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
"The store_serialized_dags parameter has been deprecated. "
                "You should pass the read_dags_from_db parameter.",
                DeprecationWarning,
                stacklevel=2,
            )
            read_dags_from_db = store_serialized_dags
        dag_folder = dag_folder or settings.DAGS_FOLDER
        self.dag_folder = dag_folder
        self.dags: Dict[str, DAG] = {}
        
        self.file_last_changed: Dict[str, datetime] = {}
        self.import_errors: Dict[str, str] = {}
        self.has_logged = False
        self.read_dags_from_db = read_dags_from_db
        
        self.dags_last_fetched: Dict[str, datetime] = {}
        
        self.dags_hash: Dict[str, str] = {}
        self.dagbag_import_error_tracebacks = conf.getboolean('core', 'dagbag_import_error_tracebacks')
        self.dagbag_import_error_traceback_depth = conf.getint('core', 'dagbag_import_error_traceback_depth')
        self.collect_dags(
            dag_folder=dag_folder,
            include_examples=include_examples,
            include_smart_sensor=include_smart_sensor,
            safe_mode=safe_mode,
        )
        
        
        self.load_op_links = load_op_links
    def size(self) -> int: