Add entry for skipping QA in PR template

[yzhan289]

What does this PR do?

Update the Github PR template to include using the qa/skip-qa label.

Motivation

This label lets the release script directly skip labeled PRs from having trello cards generated rather than having a prompt.

Additional Notes

Credit to @FlorentClarret for finding this in the script

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [ ] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [ ] PR must have changelog/ and integration/ labels attached