ref-manual: system-requirements: Ubuntu 22.04 now supported
Following its addition to meta-poky/conf/distro/poky.conf
https://git.yoctoproject.org/poky/commit/?id=7786b09212d6ab582db39d0d7d1a4209d36db2ba
(From yocto-docs rev: 393e9ae7c37544fd5c2841d99dd9bcd6db03dbbd)
Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>