Use the 'workflow::in dev' label instead of the pingpong label

What does this MR do and why?

This replaces the use of the ~"🏓" label in favor of the more explicit workflowin dev label, as discussed in Slack and !1387 (comment 954183380).

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

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

Follow-up items

• Open a one-off MR to add workflowin dev to Community contribution that currently have ~"🏓" set (and remove ~"🏓" from them)