Improve binary-size CI

[diondokter]

The binary-size job compiles the master branch and the PR branch, then feeds both elf files to bloaty and posts a comment in the PR with te results.

There are three major issues:

1. The comment triggers notifications. It's not that important, I wish that could be turned off somehow
2. A new comment is posted every time. It'd be better to update the comment if there already is one
3. The comments aren't posted at all when someone else opens the PR. This has to do with permissions. You can get around it, but I don't fully know what the ramifications are.

[praseodym]

2. A new comment is posted every time. It'd be better to update the comment if there already is one

You can use the Sticky Pull Request Comment action for that, which will update the existing comment when the workflow gets re-run. Example usage from Abacus: https://github.com/kiesraad/abacus/blob/d220eb9f2b857ea4fdaa7ed7f2e1e7a994ac1a1b/.github/workflows/pdf-diff.yml#L60-L68