scripts: sphinx-pre-install: add a missing f-string marker

scripts: sphinx-pre-install: add a missing f-string marker

I forgot one f-string marker, with turned to be affecting 3
lines, because of cut-and-paste ;-)

Use the proper f-string marker to print Sphinx version at
the hint lines. Yet, we don't want to print as a tuple, so
call ver_str() for it.

Ideally, we would be placing it directly at the f-string, but
Python 3.6 f-string support was pretty much limited. Only
3.12 (PEP 701) makes it similar to Perl, allowing expressions
inside it. It sounds that function call itself was introduced
on 3.7.

As we explicitly want this one to run on 3.6, as latest Leap
comes with it, we can't use function calls on f-string.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/b0ad1795446b17a00ba2dd83f366e784253668e6.1754992972.git.mchehab+huawei@kernel.org