**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
path_hash = hashlib.sha1(filepath.encode('utf-8')).hexdigest()
        mod_name = f'unusual_prefix_{path_hash}_{org_mod_name}'
        if mod_name in sys.modules:
            del sys.modules[mod_name]
        timeout_msg = f"DagBag import timeout for {filepath} after {self.DAGBAG_IMPORT_TIMEOUT}s"
        with timeout(self.DAGBAG_IMPORT_TIMEOUT, error_message=timeout_msg):
            try:
                loader = importlib.machinery.SourceFileLoader(mod_name, filepath)
                spec = importlib.util.spec_from_loader(mod_name, loader)
                new_module = importlib.util.module_from_spec(spec)
                sys.modules[spec.name] = new_module
                loader.exec_module(new_module)
                return [new_module]
            except Exception as e:  
                self.log.exception("Failed to import: %s", filepath)
                if self.dagbag_import_error_tracebacks:
                    self.import_errors[filepath] = traceback.format_exc(
                        limit=-self.dagbag_import_error_traceback_depth
                    )
                else:
                    self.import_errors[filepath] = str(e)
        return []
    def _load_modules_from_zip(self, filepath, safe_mode):
        mods = []
        with zipfile.ZipFile(filepath) as current_zip_file:
            for zip_info in current_zip_file.infolist():
                head, _ = os.path.split(zip_info.filename)
                mod_name, ext = os.path.splitext(zip_info.filename)
                if ext not in [".py", ".pyc"]:
                    continue