Enable merge queues

[lagergren]

Adds some smoothness, allowing things like "merge this to master when the test are green", I am going to bed, and more importantly, it makes sure to serialize any publications / tagging moves that go into master, to ensure that there aren't collisions between branches that publish at the same time. This should not be possible with different master GitHub runners executing at the same time anyway, but the merge queue will ensure this 100%, and it also saves us time to manually poll if our tests are through and everything is approved, and then manually hitting merge.