Broken shared linked crosshair tool if set on one dimension only

[TheoMathurin]

ALL software version info

Software Version Info

```plaintext holoviews 1.19.1 bokeh 3.5.2 panel 1.15.0 ```

Description of expected behavior and the observed behavior

The update to Bokeh 3.5 breaks shared Crosshair tools seemingly if they're not enabled for both width and height. Separate tools appear separately on each plot.

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

NB: Pure bokeh example from their docs works as expected.

import holoviews as hv
import numpy as np
from bokeh.models import CrosshairTool, Span
import panel as pn

hv.extension("bokeh")

s1 = hv.Scatter(np.random.randn(10, 10))
s2 = hv.Scatter(np.random.randn(10, 10))
s3 = hv.Scatter(np.random.randn(10, 10))
s4 = hv.Scatter(np.random.randn(10, 10))

height = Span(dimension="height")
width = Span(dimension="width")
cht1 = CrosshairTool(overlay=[height, width])
cht2 = CrosshairTool(overlay=height)
s1 = s1.opts(tools=[cht1])
s2 = s2.opts(tools=[cht1])
s3 = s3.opts(tools=[cht2])
s4 = s4.opts(tools=[cht2])

pn.Row(pn.Column(s1, s2), pn.Column(s3, s4)).servable()

Stack traceback and/or browser JavaScript console output

Nothing

Screenshots or screencasts of the bug in action

[hoxbro]

Introduced by https://github.com/holoviz/holoviews/pull/6220