Handle foreign key violation with savepoint

Apparently wrapping a potential database error in an eval doesn't prevent
DBIx::Class from aborting the transaction.

But with a SAVEPOINT we can wiork around that.
svp_rollback will set back the transaction to the sate from svp_begin.

Issue: https://progress.opensuse.org/issues/124487

lib/OpenQA/Shared/Plugin/Gru.pm

@@ -144,6 +144,7 @@ sub _find_existing_minion_job ($self, $task, $args, $job_ids) {
 
 sub _add_jobs_to_gru_task ($self, $gru_id, $job_ids) {
     my $schema = OpenQA::Schema->singleton;
+    $schema->svp_begin('try_gru_dependencies');
     for my $id (@$job_ids) {
         # Add job to existing gru task with the same args
         my $gru_dep = eval { $schema->resultset('GruDependencies')->create({job_id => $id, gru_task_id => $gru_id}); };
@@ -155,9 +156,11 @@ sub _add_jobs_to_gru_task ($self, $gru_id, $job_ids) {
             # if the GruTask was already deleted meanwhile, we can skip
             # the rest of the jobs, since the wanted task was done
             log_debug("GruTask $gru_id already gone, skip assigning jobs (message: $error)");
+            $schema->svp_rollback('try_gru_dependencies');
             last;
         }
     }
+    $schema->svp_release('try_gru_dependencies');
 }
 
 sub enqueue ($self, $task, $args = [], $options = {}, $jobs = []) {