Extended support for netbsd-7

[Martin Husemann <martin%NetBSD.org@localhost>]

The NetBSD project usually supports the latest release (currently 9.0)
plus the latest release of the previous release branch (currently 8.2).

Today would have been the day when the pre-previous release branch (netbsd-7)
had gone out of support.

This branch is very old - the first release, 7.0, happened September 25, 2015.
Many important security fixes are missing on this branch, so for quite some
time now we have been urging users to switch to newer supported releases.

However, when the whole world is in a global state of lockdown due to the
ongoing COVID19 pandemy, it is not the right time to trigger last minute
actions that might have forced someone to leave their safe home and head
to the computer center and update servers.

We strongly believe our users are sane and have migrated important
systems already, so noone would actually fall for this kind of trap,
but just to make sure the project decided to keep support for this
branch active for another three months (for now).

Stay safe and healthy!

Martin