Chore Dependabot settings to group GHA

[Borda]

This pull request updates the Dependabot configuration to better organize dependency update pull requests and streamline their management. The main changes involve adjusting labels, limiting the number of open pull requests, and grouping updates for GitHub Actions.

Dependabot configuration improvements:

• Changed the label for dependency update pull requests from "CI" to "dependencies" to more accurately reflect their purpose.
• Removed deprecated reviewers field so that pull requests are no longer automatically assigned to "borda". [1] [2]

GitHub Actions update management:

• Reduced the maximum number of open pull requests for GitHub Actions from 5 to 1, helping to avoid PR clutter.
• Introduced grouping for GitHub Actions updates using the groups key, so related updates are bundled together.