v20241216-184119

mandate IMDSv2 on all new ec2 runners (#6061)

This follows the removal of all IMDSv1 calls weeks ago, as well as the
upgrade of sccache on all repos that use it.

test plan: 

We'll monitor impact, but current IMDSv1 calls are close to 0, with
those left being ones based of a main older than a few weeks.

mitigation in case of failure:
- revert this
-
**https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/configuring-IMDS-existing-instances.html#modify-restore-IMDSv1**
for existing runners