consider avoid running workflows AFTER merging PRs

[plebhash]

most of our CI workflows are set to that we run them before and after PRs are merged

on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

I'm not sure about the motivation for running them after the PRs have already been merged... personally speaking, I never really check that, I only care about CI before the PRs are merged (as a safeguard against introducing bugs etc)

given that our repo can only run a limited number of workflows at the same time, this is actually introducing a significant bottleneck that severely slows down the process of merging PRs, especially when there's multiple PRs already approved and buffered for merging

unless I'm missing some important detail for the motivation for this, IMO we should stop running workflows after the PRs have been merged