Fix hv.help when pattern is set

[maximlt]

I think this was just totally untested so the code was not being updated. I've added a minimal test.

For reference this allows to get an highlighted help if the pattern matches some text:

import holoviews as hv
hv.extension('bokeh')
hv.help(hv.Curve, pattern='border')

cc @jlstevens

[jlstevens]

Looks good to me! Ready to merge?

[maximlt]

Yep!

[github-actions]

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