[BUG] whitespace on DataTable when merge_duplicate_headers= True

[e-wallace]

Describe your context
To reproduce run the following. Toggle merge_duplicate_headers= True

import dash
import pandas as pd
import dash_design_kit as ddk
from dash import dash_table

data = {
    "indication": ["Indication 1", "Indication 2"],
    "y1-450-mg-iv": [100, 200],
    "y1-900-mg-iv": [150, 250],
    "y1-300-mg-sc": [120, 220],
    "y1-600-mg-sc": [130, 230],
    "y1-1800-mg-obi": [140, 240],
    "y1-1200-mg-obi": [160, 260],
    "y1-900-mg-obi": [170, 270],
    "y1-600-mg-obi": [180, 280],
    "y2-450-mg-iv": [105, 205],
    "y2-900-mg-iv": [155, 255],
    "y2-300-mg-sc": [125, 225],
    "y2-600-mg-sc": [135, 235],
    "y2-1800-mg-obi": [145, 245],
    "y2-1200-mg-obi": [165, 265],
    "y2-600-mg-obi": [185, 285]
}

fr_posology_table_data = pd.DataFrame(data)

app = dash.Dash(__name__)

app.layout = dash_table.DataTable(
                    id='posology-data',
                    data=fr_posology_table_data.to_dict('records'),
                    columns=[
                        {'id': 'indication', 'name': ['', 'Indication'], 'type': 'text', 'editable': False},
                        {'id': 'y1-450-mg-iv', 'name': ['Year 1', '450 mg IV'], 'type': 'numeric'},
                        {'id': 'y1-900-mg-iv', 'name': ['Year 1', '900 mg IV'], 'type': 'numeric'},
                        {'id': 'y1-300-mg-sc', 'name': ['Year 1', '300 mg SC'], 'type': 'numeric'},
                        {'id': 'y1-600-mg-sc', 'name': ['Year 1', '600 mg SC'], 'type': 'numeric'},
                        {'id': 'y1-1800-mg-obi', 'name': ['Year 1', '1800 mg OBI'], 'type': 'numeric'},
                        {'id': 'y1-1200-mg-obi', 'name': ['Year 1', '1200 mg OBI'], 'type': 'numeric'},
                        {'id': 'y1-900-mg-obi', 'name': ['Year 1', '900 mg OBI'], 'type': 'numeric'},
                        {'id': 'y1-600-mg-obi', 'name': ['Year 1', '600 mg OBI'], 'type': 'numeric'},
                        {'id': 'y2-450-mg-iv', 'name': ['Year 2', '450 mg IV'], 'type': 'numeric'},
                        {'id': 'y2-900-mg-iv', 'name': ['Year 2', '900 mg IV'], 'type': 'numeric'},
                        {'id': 'y2-300-mg-sc', 'name': ['Year 2', '300 mg SC'], 'type': 'numeric'},
                        {'id': 'y2-600-mg-sc', 'name': ['Year 2', '600 mg SC'], 'type': 'numeric'},
                        {'id': 'y2-1800-mg-obi', 'name': ['Year 2', '1800 mg OBI'], 'type': 'numeric'},
                        {'id': 'y2-1200-mg-obi', 'name': ['Year 2', '1200 mg OBI'], 'type': 'numeric'},
                        {'id': 'y2-600-mg-obi', 'name': ['Year 2', '600 mg OBI'], 'type': 'numeric'}
                    ],
                    fixed_columns={'headers': True, 'data': 1},
                    style_table={'minWidth': '100%', 'maxWidth': '100%'},
                    editable = True,
                    merge_duplicate_headers= True
                )

if __name__ == '__main__':
    app.run_server(debug=True)

requirements.txt

dash-design-kit==1.9.0
dash==2.14.1
gunicorn==20.0.4
pandas>=1.1.5

Describe the bug

When merge_duplicate_headers= True there is a large amount of whitespace to the right of the table. It is visible when going to the boundary of the scroll bar. This issue is present with both dash_table.DataTable and ddk.DataTable

Expected behavior
The boundary is expected to be at the end of the last column of the dataTable.

Screenshots
Here you can see the whitespace