workflow: find merge conflicts

[yaauie]

Release notes

[rn:skip]

What does this PR do?

since mergify creates commits with merge conflicts, having a check that calls out the conflict can be helpful in cases where the conflict doesn't otherwise break the build.

Why is it important/What is the impact to the user?

No user impact.

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have commented my code, particularly in hard-to-understand areas
• ~~[ ] I have made corresponding changes to the documentation~~
• ~~[ ] I have made corresponding change to the default configuration files (and/or docker env variables)~~
• ~~[ ] I have added tests that prove my fix is effective or that my feature works~~

[mergify[bot]]

This pull request does not have a backport label. Could you fix it @yaauie? 🙏 To fixup this pull request, you need to add the backport labels for the needed branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.
• If no backport is necessary, please add the backport-skip label