### 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)

ready = multiprocessing.connection.wait(self.waitables.keys(), timeout=poll_time)
            if self._direct_scheduler_conn is not None and self._direct_scheduler_conn in ready:
                agent_signal = self._direct_scheduler_conn.recv()
                self.log.debug("Received %s signal from DagFileProcessorAgent", agent_signal)
                if agent_signal == DagParsingSignal.TERMINATE_MANAGER:
                    self.terminate()
                    break
                elif agent_signal == DagParsingSignal.END_MANAGER:
                    self.end()
                    sys.exit(os.EX_OK)
                elif agent_signal == DagParsingSignal.AGENT_RUN_ONCE:
                    
                    pass
                elif isinstance(agent_signal, CallbackRequest):
                    self._add_callback_to_queue(agent_signal)
                else:
                    raise ValueError(f"Invalid message {type(agent_signal)}")
            if not ready and not self._async_mode:
                
                
                
                
                
                self.log.warning(
                    "wait() unexpectedly returned nothing ready after infinite timeout (%r)!", poll_time
                )
                continue
            for sentinel in ready:
                if sentinel is self._direct_scheduler_conn:
                    continue