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 work around that.
svp_rollback will set back the transaction to the sate from svp_begin.

For being able to use savepoints we have to be in a transaction, and we don't
have that ensured in all our unit tests, so this is adding another txn_do
which will do nothing if it's nested.

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

lib/OpenQA/Shared/Plugin/Gru.pm

@@ -144,20 +144,29 @@ 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;
-    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 => $gru_id}); };
-        unless ($gru_dep) {
-            my $error = $@;
-            die $error
-              unless $error
-              =~ m/insert or update on table "gru_dependencies" violates foreign key constraint "gru_dependencies_fk_gru_task_id"/i;
-            # 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)");
-            last;
-        }
-    }
+    # Wrap in txn_do so we can use savepoints in the method. Necessary for cases
+    # where we are not in a transaction. Otherwise it's a noop
+    $schema->txn_do(
+        sub {
+            $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 => $gru_id}); };
+                unless ($gru_dep) {
+                    my $error = $@;
+                    $schema->svp_rollback('try_gru_dependencies');
+                    die $error
+                      unless $error
+                      =~ m/insert or update on table "gru_dependencies" violates foreign key constraint "gru_dependencies_fk_gru_task_id"/i;
+                    # 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)");
+                    last;
+                }
+            }
+            $schema->svp_release('try_gru_dependencies');
+        });
 }
 
 sub enqueue ($self, $task, $args = [], $options = {}, $jobs = []) {