Forwarded: https://jira.mariadb.org/browse/MDEV-34788?
This seems to be flaky tests and not inherently a blocker for the i386 rebuild. These issues seem like a duplicate of https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1052838 "mariadb: FTBFS multiple archs: Post-build tests randomly fail on reserved port due to lacking builder isolation" and are sporadic by nature, so they will go away on a new rebuild when the build host is less congested. Also https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1077524 is a duplicate of the same issue. I am pinging upstream now if they have ideas on how to debug this.
