chore: Added dependabot for GitHub Actions

[ydah]

Fixes

How about using dependabot in this way? When this works, a pull request is created as follows:

• ruby/bigdecimal#242

It was created with reference to the following:

• ruby/csv#265

Checklist

• [x] I acknowledge that all my contributions will be made under the project's license
• [x] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [x] I have read the Contribution Guidelines and my PR follows them
• [x] I have titled the PR appropriately
• [x] I have updated my branch with the main branch
• [-] I have added tests that prove my fix is effective or that my feature works
• [-] I have added the necessary documentation about the functionality in the appropriate .md file
• [-] I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.