Update Renovate Nuget config to group bunit dependencies

[jattasNI]

Pull Request

🤨 Rationale

Now that we established Renovate to update nuget deps in #1675 I noticed on the dependency dashboard #1537 that the 3 bunit dependencies will be updated in separate PRs. We want them to be updated together.

Here's what the dependency dashboard showed before this change:

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👩‍💻 Implementation

Add a package rule for any nuget package that starts with "bunit".

I considered grouping all minor/patch nuget dependencies in one group to reduce the PR noise, similar to what we did for npm. We may yet decide to do this but I wanted to get some runtime with the default configuration and hear the team's feedback first.

🧪 Testing

I will inspect the dashboard when this completes to ensure it works as intended.

✅ Checklist

• I have updated the project documentation to reflect my changes or determined no changes are needed.

[jattasNI]

@rajsite I bypassed you on this one too in the interest of getting our Nuget config to a better place before PRs start getting created next week.