Python: bump minimum sphinx version to 3.4.3

With RHEL 8 support retired (It's been two years since RHEL9 released),
our very oldest build platform version of Sphinx is now 3.4.3; and
keeping backwards compatibility for versions as old as v1.6 when using
domain extensions is a lot of work we don't need to do.

This patch is motivated by my work creating a new QAPI domain, which
unlike the dbus documentation, cannot be allowed to regress by creating
a "dummy" doc when operating under older sphinx versions. Easier is to
raise our minimum version as far as we can push it forwards, reducing my
burden in creating cross-compatibility hacks and patches.

A sampling of sphinx versions from various distributions, courtesy
https://repology.org/project/python:sphinx/versions

Alpine 3.16: v4.3.0 (QEMU support ended 2024-05-23)
Alpine 3.17: v5.3.0
Alpine 3.18: v6.1.3
Alpine 3.19: v6.2.1
Ubuntu 20.04 LTS: EOL
Ubuntu 22.04 LTS: v4.3.2
Ubuntu 22.10: EOL
Ubuntu 23.04: EOL
Ubuntu 23.10: v5.3.0
Ubuntu 24.04 LTS: v7.2.6
Debian 11: v3.4.3 (QEMU support ends 2024-07-xx)
Debian 12: v5.3.0
Fedora 38: EOL
Fedora 39: v6.2.1
Fedora 40: v7.2.6
CentOS Stream 8: v1.7.6 (QEMU support ended 2024-05-17)
CentOS Stream 9: v3.4.3
OpenSUSE Leap 15.4: EOL
OpenSUSE Leap 15.5: 2.3.1, 4.2.0 and 7.2.6

RHEL9 / CentOS Stream 9 becomes the new defining factor in staying at
Sphinx 3.4.3 due to downstream offline build requirements that force us
to use platform Sphinx instead of newer packages from PyPI.

Signed-off-by: John Snow <jsnow@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20240703175235.239004-2-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
2 files changed