docs: kernel-doc: avoid script crash on ancient Python

docs: kernel-doc: avoid script crash on ancient Python

While we do need at least 3.6 for kernel-doc to work, and at least
3.7 for it to output functions and structs with parameters at the
right order, let the python binary be compatible with legacy
versions.

The rationale is that the Kernel build nowadays calls kernel-doc
with -none on some places. Better not to bail out when older
versions are found.

With that, potentially this will run with python 2.7 and 3.2+,
according with vermin:

	$ vermin --no-tips -v ./scripts/kernel-doc
	Detecting python files..
	Analyzing using 24 processes..
	2.7, 3.2     /new_devel/v4l/docs/scripts/kernel-doc
	Minimum required versions: 2.7, 3.2

3.2 minimal requirement is due to argparse.

The minimal version I could check was version 3.4
(using anaconda). Anaconda doesn't support 3.2 or 3.3
anymore, and 3.2 doesn't even compile (I tested compiling
Python 3.2 on Fedora 42 and on Fedora 32 - no show).

With 3.4, the script didn't crash and emitted the right warning:

	$ conda create -n py34 python=3.4
	$ conda activate py34
	python --version
        Python 3.4.5
        $ python ./scripts/kernel-doc --none include/media
	Error: Python 3.6 or later is required by kernel-doc
	$ conda deactivate

	$ python --version
	Python 3.13.5
        $ python ./scripts/kernel-doc --none include/media
	(no warnings and script ran properly)

Supporting 2.7 is out of scope, as it is EOL for 5 years, and
changing shebang to point to "python" instead of "python3"
would have a wider impact.

I did some extra checks about the differences from 3.2 and
3.4, and didn't find anything that would cause troubles:

	grep -rE "yield from|asyncio|pathlib|async|await|enum" scripts/kernel-doc

Also, it doesn't use "@" operator. So, I'm confident that it
should run (producing the exit warning) since Python 3.2.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/87d55e76b0b1391cb7a83e3e965dbddb83fa9786.1753806485.git.mchehab+huawei@kernel.org