ci: re-fix size report

[ferferga]

Follow-up of #11203 (see this comment)

• comment_tag comes last so GH Actions interpreter doesn't trip with special characters from the previous' input
• The action already encloses the tag with the appropiate hidden markers

[ferferga]

@sxzz I'm astonished by seeing that for some reason this is not working. I'm completely out of ideas right now.

Check this run for this PR

If I recreate the exact same conditions in my fork by merging that branch with the main branch (up to date with current commit) in my fork with this PR, the run works successfully.

[sxzz]

Seems like github.event.workflow_run.pull_requests[0].number requires write permission of the repo