update github actions checkout to v3

[rosesyrett]

I get the following error message when CI runs on PRs, e.g. on #1118:

Node.js 12 actions are deprecated. Please update the following actions to use Node.js 16: actions/checkout@v2. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/.

This happens for the jobs: lint, build and test (3.9). Looking at (the github actions page)[https://github.com/marketplace/actions/checkout] for this action, updating to v3 would solve this problem.

Do we use this as an opportunity to integrate dependabot so we don't have to do this stuff manually?

[coretl]

When we adopt skeleton fully into ophyd we will get this: https://github.com/bluesky/python3-pip-skeleton/blob/main/.github/dependabot.yml. I think we need tickets for adopting skeleton into ophyd and bluesky (event model is already done)