Removing commit msg checkbox from PR template

[john-science]

What is the change?

Removed one checkbox from the PR template:

• The commit message(s) follow good practices.

Why is the change being made?

We have a squash-and-merge policy for ARMI PRs. So I don't care if you have some silly PR messages in the history of your feature branch.

---

Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify any new/changed code.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes have been updated if necessary.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in pyproject.toml.

[opotowsky]

I trust you to rephrase the sentence I commented on to your liking. Approved!