Use SummaryBuilder instead of IssueBuilder

What does this MR do and why?

Use SummaryBuilder instead of IssueBuilder

In gitlab-org/ruby/gems/gitlab-triage!255 (merged) we renamed it so we need to follow the same change.

Expected impact & dry-runs

I triggered a dry-run for the schedule and I think it's working: https://gitlab.com/gitlab-org/quality/triage-ops/-/pipelines/657846169

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review

Closes #1136 (closed)