### What?
When the router action queue receives a bunch of async actions in quick succession, some of those requests are dropped, and as a result, anything observing pending transitions will be stuck in a pending state.
### Why?
When adding items to the action queue, the intended behavior is for new actions to be added to the end of the action queue, to be picked up by `runRemainingActions` once the in-flight action is processed. However, new actions are erroneously overwriting pending actions in the queue rather than appending them, as `actionQueue.last` might have a pending action attached to it.
### How?
This moves the assignment of `actionQueue.last` to always be in `dispatchAction`, rather than the function that processes the action, so that we always have a single spot where `last` is assigned and to prevent it from erroneously omitted/overwritten.
Fixes#59011
298bbe5489