Jeff King
00fa850235
Debian 11 just recently went out of its LTS period, and is unmaintained
by the project (there is "Extended LTS", but it is a paid service
provided by a third party).
The point of the debian-11 job was to cover older releases in the LTS
state, per ac112fd4f0 (Add additional CI jobs to avoid accidental
breakage, 2024-10-31). Bumping to debian-12 will cover us there for the
next 2 years.
Signed-off-by: Jeff King <peff@peff.net>