### 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)

pass
    @property
    def start_time(self):
        return DEFAULT_DATE
    @property
    def pid(self):
        return 1234
    @property
    def done(self):
        return True
    @property
    def result(self):
        return self._result
    @staticmethod
    def _create_process(file_path, callback_requests, dag_ids, dag_directory, pickle_dags):
        return FakeDagFileProcessorRunner(
            file_path,
            pickle_dags,
            dag_ids,
            dag_directory,
            callback_requests,
        )
    @property
    def waitable_handle(self):
        return self._waitable_handle
class TestDagFileProcessorManager: