In the meantime postgresql-14 has been accepted into Debian/experimental:
https://buildd.debian.org/status/logs.php?pkg=postgresql-14&ver=14%7Ebeta1-1
Interestingly, the test is only failing on i386 and none of the other
architectures, which could hint at 80-bit extended precision FP
problems.
(The sparc64 error there is something else, I'll try rerunning it.
command failed: "psql" -X -c "CREATE DATABASE \"isolation_regression\" TEMPLATE=template0" "postgres")
Christoph