[Breaking Change][PR Workflow] REST API Breaking Changes PR check should check who added the suppression label

PRs in the azure-rest-api-specs repo are blocked from merging if the Breaking Changes PR check reports a failure. But the result of the Breaking Changes check is squashed if the "Approved-BreakingChange" label has been added to the PR. That label is supposed to signify that the PR was reviewed by the Breaking Change review board and determined to be an allowable change.

Unfortunately, there is no means to prevent _any_ user with labelling permissions to add the "Approved-BreakingChange" label, so changes that should not be permitted are allowed to merge, resulting in customer disruption.

An example is [PR 23647](https://github.com/Azure/azure-rest-api-specs/pull/23647).

Since we cannot restrict who can add the label, I think the PR check must only be squashed if the label was added by a member of the breaking change review board or otherwise trained and responsible user.