[9.18] chg: ci: Allow re-run of the shotgun jobs to reduce false positives

The false positive rate is about 10-20 % when evaluating shotgun results
from a single run. Attempt to reduce the false positive rate by allowing
a re-run of failed jobs.

Backport of MR !10271

Merge branch 'backport-nicki/ci-shotgun-reduce-false-positives-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!10280