[CI] Some commits (force push, update with main?) trigger wrong reviewer requests & labelling

[svrnm]

I saw this happening a few times now, but I am not 100% sure how this happens, and we need to investigate:

if a contributor updates their PR with the latest main (force push for example), sometimes the actions for labelling and requesting reviews get triggered in a way that they request reviews and add labels across all files that have been part of that rebase. I am not 100% sure how to address that, but I wanted to record it as a bug.

Example: #5575

Run examples:
https://github.com/open-telemetry/opentelemetry.io/actions/runs/11949606337/job/33309393503?pr=5575

Related bug in the labeler action:

actions/labeler#784

[svrnm]

We might want to restrict the action types in the workflow files, e.g. exclude synchronize ("A pull request's head branch was updated. For example, the head branch was updated from the base branch or new commits were pushed to the head branch."), via https://docs.github.com/en/webhooks/webhook-events-and-payloads?actionType=synchronize#pull_request

[svrnm]

By default, a workflow only runs when a pull_request_target event's activity type is opened, synchronize, or reopened.

So we should change that to opened and reopened