Do not auto credit when uploading an image

Problem/Motivation

I have seen a lot of people uploading useless screenshots of console output that a patch for example applies. For some users that's the only contribution they are doing. I think it's okay that they do it, but I find it harsh that they get automatically credited for it. While other users who are actively participating in an issue and reviewing it might not be selected for an issue credit.

There are big name companies that are doing this to score many contributions on their profiles, which is a bit lame to be honest because there are many users who actively help to resolve issues by testing and reviewing them but don't always end up with an issue credit.

Here is an example: https://www.drupal.org/project/drupal/issues/784672#comment-14128359

Why would it be fair to be credited for uploading a useless screenshot, while active contributors wouldn't be credited?

Steps to reproduce

Simply upload an image to an issue and post. You will see that the "credit checkbox" is automatically checked for that user now.

Proposed resolution

Exclude uploading images from getting an automatic credit. .patch files and others should still auto credit. If the image adds value a maintainer can still credit a user for it.

Remaining tasks

Update crediting logic.

User interface changes

Uploading images no longer auto credits.

API changes

N/A

Data model changes

N/A