Minor dependabot auto-merge workflow improvements

[patinthehat]

This PR improves the auto-merge workflow to be more succinct and readable, as well as making the steps more clear in terms of what their function is at a glance.

• The two separate auto-merge steps for patch and minor updates has been merged into a single step.
• The auto-merge step (both description and logic) for GitHub actions with a compatibility score of 90%+ has been simplified

[patinthehat]

ping @freekmurze