fix: test: rndc test: second 'rndc reconfig' happens too soon

Rndc test "test 'rndc reconfig' with a broken config" was failing
intermittently.

Wait for 'running' to be logged rather than just using 'sleep 1' before
calling 'rndc reconfig' a second time to get the expected error message
rather than 'reconfig request ignored: already running'.

Closes #5408

Merge branch '5408-rndc-test-second-rndc-reconfig-happens-too-soon' into 'main'

See merge request isc-projects/bind9!10687