[9.20] chg: ci: Disable Kerberos in tumbleweed

In the tumbleweed image, we utilize LibreSSL. Several BIND 9 libraries
are linked against LibreSSL's libcrypto.so.55, and when Kerberos is
enabled, we link against libk5crypto.so.3, which in turn links against
OpenSSL's libcrypto.so.3. This might theoretically lead to a symbol
conflict.

Closes #5394

Backport of MR !10643

Merge branch 'backport-5394-disable-kerberos-in-tumbleweed-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!10651