wendelin.core: v↑ 2.0.alpha3 -> 2.0.alpha3.post7

Since the wendelin.core 2.alpha3 release 9 month ago, new fixes
were added to wendelin.core, which we would like to have in SlapOS.
One very important new feature is that this wendelin.core version now
support golang 1.20, so with this we can easily proceed to upgrade our
default golang version.

/reviewed-by @kirr
/reviewed-on nexedi/slapos!1416