Remove action runners on user deletion (#27902) (#27908)

Backport #27902 by @earl-warren

- On user deletion, delete action runners that the user has created.
- Add a database consistency check to remove action runners that have
nonexistent belonging owner.
- Resolves https://codeberg.org/forgejo/forgejo/issues/1720

(cherry picked from commit 009ca7223d)

Co-authored-by: Earl Warren <109468362+earl-warren@users.noreply.github.com>
Co-authored-by: Gusted <postmaster@gusted.xyz>

models/actions/runner.go

@@ -266,3 +266,27 @@ func CreateRunner(ctx context.Context, t *ActionRunner) error {
 	_, err := db.GetEngine(ctx).Insert(t)
 	return err
 }
+
+func CountRunnersWithoutBelongingOwner(ctx context.Context) (int64, error) {
+	// Only affect action runners were a owner ID is set, as actions runners
+	// could also be created on a repository.
+	return db.GetEngine(ctx).Table("action_runner").
+		Join("LEFT", "user", "`action_runner`.owner_id = `user`.id").
+		Where("`action_runner`.owner_id != ?", 0).
+		And(builder.IsNull{"`user`.id"}).
+		Count(new(ActionRunner))
+}
+
+func FixRunnersWithoutBelongingOwner(ctx context.Context) (int64, error) {
+	subQuery := builder.Select("`action_runner`.id").
+		From("`action_runner`").
+		Join("LEFT", "user", "`action_runner`.owner_id = `user`.id").
+		Where(builder.Neq{"`action_runner`.owner_id": 0}).
+		And(builder.IsNull{"`user`.id"})
+	b := builder.Delete(builder.In("id", subQuery)).From("`action_runner`")
+	res, err := db.GetEngine(ctx).Exec(b)
+	if err != nil {
+		return 0, err
+	}
+	return res.RowsAffected()
+}