Suggestion: Do not subtract from approvals if there were no code changes

[lorenzleutgeb]

When someone very clearly expresses their approval in a comment, but does not use the GitHub feature to signal approval, I sometimes increase the label-based approval counter myself (to attract attention of potential mergers). Of course I could ask the person that commented favorably but did not use the GitHub feature to do exactly that, but this requires another roundtrip (I comment, they receive a notification on their end, they approve, and only then future runs will increase the label-based counter, or I do it myself).

I noticed that in these cases, the tool sometimes decreases the number of approvals, see e.g. NixOS/nixpkgs#311986 where there was approval clearly expressed in a comment, I set the label, and later @wegank ran the tool which decreased the counter.

I therefore propose that under the condition that there were no new commits in the PR, the number of approvals should not be decreased automatically.

If people that increase the label-based approval counter manually (like I do) are honest, this should work out pretty nicely.