Export to markdown only contains H2 headers

### Bug
I tried loading a pdf file with multiple headings / sections. But seems like docling always extracts it to markdown with H2 (##) only. Am I doing something wrong here? I have tried with multiple PDFs.

[docling_test.pdf](https://github.com/user-attachments/files/18872099/docling_test.pdf)

...

### Steps to reproduce
import logging
import time
from pathlib import Path

from docling_core.types.doc import ImageRefMode, PictureItem, TableItem
from docling.datamodel.base_models import FigureElement, InputFormat, Table
from docling.datamodel.pipeline_options import PdfPipelineOptions, TableFormerMode, EasyOcrOptions, TesseractOcrOptions
from docling.document_converter import DocumentConverter, PdfFormatOption

_log = logging.getLogger(__name__)

IMAGE_RESOLUTION_SCALE = 2.0

def main():
logging.basicConfig(level=logging.INFO)

input_doc_path = Path("/Users/nikhildi/Downloads/solution.pdf")

output_dir = Path("scratch")
pipeline_options = PdfPipelineOptions()
pipeline_options.do_ocr = True
pipeline_options.ocr_options = TesseractOcrOptions(lang=["eng"])
pipeline_options.generate_picture_images = False

doc_converter = DocumentConverter(
format_options={
InputFormat.PDF: PdfFormatOption(pipeline_options=pipeline_options)
}
)

start_time = time.time()

conv_res = doc_converter.convert(input_doc_path)
md_filename = output_dir / f"test.md"

print(conv_res.document.save_as_markdown(filename= md_filename, image_placeholder=""))
...

### Docling version
docling 2.15.1
docling-core 2.15.1
docling-ibm-models 3.2.1
docling-parse 3.1.1
...

### Python version
Python 3.11.11
...