Add GitHub Actions for Dependabot configuration (#5482)
Add GitHub Actions for Dependabot configuration (#5482)

`versioning-strategy` is unsupported for `github-actions`.

See also:
- https://github.com/stylelint/stylelint/pull/5481#issuecomment-899056059
- https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/configuration-options-for-dependency-updates
stylelint/stylelint,stylelint/stylelint,stylelint/stylelint,stylelint/stylelint