chg: test: For TSAN builds, use libraries from /opt/tsan

The new TSAN images, the TSAN-enabled images install libraries to
opt/tsan, synchronize the configure options and CFLAGS between gcc:tsan
and clang:tsan images and set the PKG_CONFIG_PATH to /opt/tsan/lib.

Additionally, drop Debian bullseye that's EOL now.

Merge branch 'ondrej/use-staging-tsan-images' into 'main'

See merge request isc-projects/bind9!9324