CI: Make PRs not run tests twice on each commit

[ValarDragon]

Right now CI runs tests twice for every commit on a PR. One for (push) and one for (pull request). We actually often get into a situation where the push test is done, but we're still waiting on the pull request CI test.

Is it possible to de-duplicate this? Perhaps only having tests on commit? (Do we lose anything by doing that?)

[niccoloraspa]

As you said we run the test workflow on any push to any branch and any pull_request event:

# Event that triggers the workflow
on:
  pull_request:           # any pull_request event:
  push:                   # any push to any branch 
    branches:
      - '**'	

Possible solutions to avoid duplicated runs are:

1. Don't run the workflow on pull_request event:

on:
  push:
    branches:
      - '**'	

This is super simple to do but doing so we lose the codecov report comment on PRs as in #1098 (comment).
I think that the report would still will be accessible inspecting the workflow run.

2. A more complicated solution to avoid running both on push and on pull_request would be to add a check before running the job using https://github.com/fkirc/skip-duplicate-actions.
   It would complicate a little bit the workflow and might need some tweaking to find the right configuration but it's doable. More info: https://github.com/fkirc/skip-duplicate-actions#example-1-skip-entire-jobs

---

If we don't care much about the codecov report on the comment I would go with 1 which is super simple to do. Otherwise I'll start to play around with https://github.com/fkirc/skip-duplicate-actions.

What do you think?

[ValarDragon]

I think 2 would be nice. I don't really use codecov that often, but it seems like a good thing to do / incorporate more.