Keep GitHub Actions up to date with GitHub's Dependabot

[cclauss]

Fixes some of the software supply chain safety warnings like at the bottom right of https://github.com/realm/SwiftLint/actions/runs/9627271672

• Keeping your actions up to date with Dependabot
• Configuration options for the dependabot.yml file - package-ecosystem

[SimplyDanny]

Very helpful. Thank you!

[cclauss]

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