Unnecessary axis linking

#### ALL software version info
(this library, plus any other relevant software, e.g. bokeh, python, notebook, OS, browser, etc should be added within the dropdown below.)

Software Version Info

```plaintext
hvplot 0.12.1
python 3.10
bokeh 3.8.0
Win11
Firefox
```

#### Description of expected behavior and the observed behavior
When combining two plots with distinct y data/dimension the y axis shall not be linked.
However this behavior is observed when both plots show multiple y data each. If multiple y columns are used in just one plot everything works as expected (no y linking).

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

```python
import pandas as pd
import numpy as np
import hvplot.pandas
from hvplot import hvPlot
hvplot.extension('bokeh')
from bokeh.plotting import show

df = pd.DataFrame({"a": [0, 1, 2, 3], "b": [10, 11, 12, 13], "c": [100, 101, 102, 103],
"d": [10, 11, 12, 13], "e": [20, 21, 22, 23]})

p1 = df.hvplot.line(x='a', y=['b', 'c'])
#p2 = df.hvplot.line(x='a', y='e') # this works as expected
p2 = df.hvplot.line(x='a', y=['d', 'e'])

p = (p1 + p2).cols(1)

show(hvplot.render(p))

```

#### Stack traceback and/or browser JavaScript console output

#### Screenshots or screencasts of the bug in action

- [ ] I may be interested in making a pull request to address this