### 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)

n = 0
            while True:
                if exit_event.is_set():
                    break
                req = CallbackRequest(str(dag_filepath))
                try:
                    logging.debug("Sending CallbackRequests %d", n + 1)
                    pipe.send(req)
                except TypeError:
                    
                    
                    break
                except OSError:
                    break
                n += 1
                logging.debug("   Sent %d CallbackRequests", n)
        thread = threading.Thread(target=keep_pipe_full, args=(parent_pipe, exit_event))
        fake_processors = []
        def fake_processor_(*args, **kwargs):