### 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)

)
        dag1_req2 = DagCallbackRequest(
            full_filepath="/green_eggs/ham/file1.py",
            dag_id="dag1",
            run_id="run1",
            is_failure_callback=False,
            processor_subdir=tmpdir,
            msg=None,
        )
        dag1_sla1 = SlaCallbackRequest(
            full_filepath="/green_eggs/ham/file1.py",
            dag_id="dag1",
            processor_subdir=tmpdir,
        )
        dag1_sla2 = SlaCallbackRequest(
            full_filepath="/green_eggs/ham/file1.py",
            dag_id="dag1",
            processor_subdir=tmpdir,
        )
        dag2_req1 = DagCallbackRequest(
            full_filepath="/green_eggs/ham/file2.py",
            dag_id="dag2",
            run_id="run1",
            is_failure_callback=False,
            processor_subdir=tmpdir,
            msg=None,
        )
        
        manager._add_callback_to_queue(dag1_req1)
        manager._add_callback_to_queue(dag1_sla1)