[FEATURE]: Add dependabot.yml to keep GitHub Actions dependencies updated

### Feature and its Use Cases

I was going through the repo and noticed there's no dependabot.yml
here. The workflows are using actions like actions/checkout@v4 and
actions/github-script@v7 but there's nothing to automatically update
these when new versions come out.

Simple fix - adding a dependabot.yml to auto-update GitHub Actions
dependencies weekly so we don't end up with stale action versions.

I can open a PR for this if it looks good.

### Additional Context

_No response_

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates