### 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 to check that a DAG with a system.exit() doesn't break the scheduler.
        """
        dag_id = "exit_test_dag"
        dag_directory = TEST_DAG_FOLDER.parent / "dags_with_system_exit"
        
        clear_db_dags()
        clear_db_serialized_dags()
        child_pipe, parent_pipe = multiprocessing.Pipe()
        manager = DagFileProcessorManager(
            dag_directory=dag_directory,
            dag_ids=[],
            max_runs=1,
            processor_timeout=timedelta(seconds=5),
            signal_conn=child_pipe,