docs: Restore "smart quotes" for quotes

Commit eaae7575 ("docs: turn off "smart quotes" in the HTML build")
disabled conversion of quote marks along with that of dashes.
Despite the short summary, the change affects not only HTML build
but also other build targets including PDF.

However, as "smart quotes" had been enabled for more than half a
decade already, quite a few readers of HTML pages are likely expecting
conversions of "foo" -> “foo” and 'bar' -> ‘bar’.

Furthermore, in LaTeX typesetting convention, it is common to use
distinct marks for opening and closing quote marks.

To satisfy such readers' expectation, restore conversion of quotes
only by setting smartquotes_action [1].

Link: [1] https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-smartquotes_action


Cc: stable@vger.kernel.org  # v6.4
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240225094600.65628-1-akiyks@gmail.com