### 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)

filename_to_parse = tmpdir / "temp_dag.py"
        
        with open(filename_to_parse, "w") as file_to_parse:
            file_to_parse.writelines("an invalid airflow DAG")
        child_pipe, parent_pipe = multiprocessing.Pipe()
        async_mode = "sqlite" not in conf.get("database", "sql_alchemy_conn")
        manager = DagFileProcessorManager(
            dag_directory=tmpdir,
            max_runs=1,
            processor_timeout=timedelta(days=365),
            signal_conn=child_pipe,
            dag_ids=[],
            pickle_dags=False,
            async_mode=async_mode,
        )
        with create_session() as session:
            self.run_processor_manager_one_loop(manager, parent_pipe)
            import_errors = session.query(errors.ImportError).all()
            assert len(import_errors) == 1
            filename_to_parse.remove()
            
            self.run_processor_manager_one_loop(manager, parent_pipe)
            import_errors = session.query(errors.ImportError).all()
            assert len(import_errors) == 0
            session.rollback()
        child_pipe.close()
        parent_pipe.close()
    @conf_vars({("core", "load_examples"): "False"})
    def test_max_runs_when_no_files(self):