fix: test: Fix `cyclic_glue` system test

The `cyclic_glue` system test was not explicitly waiting for the dump to
complete. As a result, the test could read an outdated dump file and
perform assertions on database state. Fix this by waiting for `dumpdb`
command to finish before reading `named_dump.db`.

Merge branch 'colin/fix-cyclic_glue-test' into 'main'

See merge request isc-projects/bind9!11934