CI: Add concurrency on actions ran on PRs

[inFocus7]

Describe the solution you'd like

I notice that none of our actions/jobs have concurrency set. This means it is possible that a pull request can have multiple running actions from older commits running at the same time, costing resources.

For example:

1. I push a commit, causing our various tests to run.
2. I push another commit while above is running, causing another set of tests to run.
3. Since we don't have any job concurrency set up, the older set of tests/actions continue running while new ones are as well.

Setting up concurrency allows us to either queue the latest commit runs, or simply cancel the previously-running actions.

There are fail-safes where maintainers have to approve runs (I believe for first-time contributors), but still worth having this for users who don't need approvals to run CI on commit.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Eraser version:
• Kubernetes version: (use kubectl version):