Make PR preview workflow still complete successfully when different PRs open at the same time

[atteggiani]

What

Currently the deploy workflow gets cancelled if another deploy workflow gets called.
This is good because it avoids a duplication of tasks (the second workflow would overwrite the first so there is no point finishing to run the first).

However, currently the PR previews are attached to a single workflow run, and if the workflow gets cancelled, the deployment preview fails.

Solution

Re-structure the workflow so that, after the deployment of all PRs (coming from any deployment workflow), it issues comments to all the PR deployed (not only to the one that triggered the workflow).