CI: Set up dependabot for GitHub Actions

[akihironitta]

Before submitting

• [x] Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• [n/a] Did you make sure to update the docs?
• [n/a] Did you write any new necessary tests?

What does this PR do?

See title.

PR review

Anyone in the community is free to review the PR once the tests have passed. If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[codecov[bot]]

Codecov Report

Merging #186 (c19a70d) into main (46d4fbc) will not change coverage. The diff coverage is n/a.

:exclamation: Current head c19a70d differs from pull request most recent head 4fec5ba. Consider uploading reports for the commit 4fec5ba to get more accurate results

@@         Coverage Diff         @@
##           main   #186   +/-   ##
===================================
  Coverage    75%    75%           
===================================
  Files         2      2           
  Lines       370    370           
===================================
  Hits        276    276           
  Misses       94     94