### Apache Airflow version

2.4.1

### What happened

When there are large number of dag files, lets say 10K and each takes sometime to parse,  dag_parser doesnt pick any newly created files till all 10k files are finished parsing

`if not self._file_path_queue:
                self.emit_metrics()
                self.prepare_file_path_queue()`

Above logic only adds new files to queue when queue is empty

### What you think should happen instead

Every loop of dag processor should pick new files and add into file for parsing queue

### How to reproduce

_No response_

### Operating System

All

### Versions of Apache Airflow Providers

_No response_

### Deployment

Docker-Compose

### Deployment details

_No response_

### Anything else

_No response_

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

"""Test DagFileProcessorManager._refresh_dag_dir method"""
        manager = DagFileProcessorManager(
            dag_directory=TEST_DAG_FOLDER,
            max_runs=1,
            processor_timeout=timedelta(days=365),
            signal_conn=MagicMock(),
            dag_ids=[],
            pickle_dags=False,
            async_mode=True,
        )
        dagbag = DagBag(dag_folder=tmpdir, include_examples=False)
        zipped_dag_path = os.path.join(TEST_DAGS_FOLDER, "test_zip.zip")
        dagbag.process_file(zipped_dag_path)
        dag = dagbag.get_dag("test_zip_dag")
        dag.sync_to_db()
        SerializedDagModel.write_dag(dag)
        manager.last_dag_dir_refresh_time = timezone.utcnow() - timedelta(minutes=10)
        manager._refresh_dag_dir()
        
        assert SerializedDagModel.has_dag("test_zip_dag")
        
        assert DagCode.has_dag(dag.fileloc)
    @conf_vars(
        {
            ("core", "load_examples"): "False",
            ("scheduler", "standalone_dag_processor"): "True",
        }
    )
    def test_fetch_callbacks_from_database(self, tmpdir):