Tiles attribution not showing when using custom tile server

[ernhollam]

ALL software version info

Software Version Info

bokeh                     3.5.2           py311h746a85d_0
cartopy                   0.22.0          py311h786e728_0
geoviews                  1.13.0          py311haa95532_0
geoviews-core             1.13.0          py311haa95532_0
holoviews                 1.19.1          py311haa95532_0
numpy                     1.26.4          py311hdab7c0b_0

Description of expected behavior and the observed behavior

When adding tile in geoviews, I expect the attribution of the underlying Bokeh model to show at the bottom right corner of the map, just like with any built-in tile server. However, it is not the case when I'm using custom tile server such as the French one. I think this might be a bug.
(Discussed at discourse post)

Complete, minimal, self-contained example code that reproduces the issue

from bokeh.plotting import figure, show
from bokeh.io import output_notebook
from bokeh.models import WMTSTileSource

output_notebook()

import cartopy.crs as ccrs
import numpy as np

import geoviews as gv
gv.extension('bokeh')

x_bounds=(2.14572, 2.61568)
y_bounds=(48.68763, 49.01233)
google_mercator_bbox = ccrs.GOOGLE_MERCATOR.transform_points(
        ccrs.PlateCarree(), x=np.array(x_bounds), y=np.array(y_bounds)
    )[:, :-1].flatten()

PLANIGNV2_tile_provider = WMTSTileSource(url="https://data.geopf.fr/tms/1.0.0/GEOGRAPHICALGRIDSYSTEMS.PLANIGNV2/{Z}/{X}/{Y}.png",
                              name='PLAN IGN',
                              attribution=""" <a href="https://www.ign.fr/" target="_blank">&copy; IGN</a> maps""",
                              max_zoom=19)

# This shows the attributions at the bottom of the map
plan_ign_v2 = figure(x_range=(google_mercator_bbox[0], google_mercator_bbox[2]),
                     y_range=(google_mercator_bbox[1], google_mercator_bbox[3]),
                     min_width=800, min_height=400,
                     x_axis_type='mercator', y_axis_type='mercator',
                     active_drag='pan', active_scroll='wheel_zoom', match_aspect=True)
plan_ign_v2.add_tile(local_PLANIGNV2_tile_provider)
show(plan_ign_v2)

# The attribution is not visible using gv.WMTS()
gv.WMTS(PLANIGNV2_tile_provider).opts(active_tools=['wheel_zoom'], min_height=500, min_width=800,
                              xlim=(google_mercator_bbox[0], google_mercator_bbox[2]),
                     ylim=(google_mercator_bbox[1], google_mercator_bbox[3]))

# However it's there with the built-in OSM tile sources
gv.tile_sources.OSM().opts(active_tools=['wheel_zoom'], min_height=500, min_width=800,
                              xlim=(google_mercator_bbox[0], google_mercator_bbox[2]),
                     ylim=(google_mercator_bbox[1], google_mercator_bbox[3]))

Screenshots

[holovizbot]

This issue has been mentioned on HoloViz Discourse. There might be relevant details there:

https://discourse.holoviz.org/t/tiles-attribution-not-showing-when-using-custom-tiles-server-with-gv-wmts/8367/3