[BUG] Workflow is not discarding exceeded events when configuring execution control limits

**Describe the bug**
When limiting concurrency to one worker and setting the queue size to 1, I expect events to be dropped when more than one event is issued simultaneously. However, instead of being discarded, the events are getting queued.

**To Reproduce**
Steps to reproduce the behavior:

1. Create a workflow with an HTTP trigger
1. Go to the workflow configuration.
2. Set concurrency to one worker.
3. Set the queue size to 1.
4. Optionally set limit execution rate to 1 execution every minute
5. Send multiple events at the same time, e.g. `curl $HTTP_URL/$COUNTER` where COUNTER increases by 1 after each request
6. Observe that the events are queued rather than being discarded.

**Expected behavior**
Events should be discarded when more than one event is issued simultaneously, given the concurrency limit of one worker and a queue size of 1.

**Screenshots**

Start at the workflow's HTTP trigger and execution-control configuration, then reproduce the issue with one worker, queue size 1, and simultaneous curl requests. Verify that events beyond the configured capacity are discarded rather than queued, including when the execution rate limit is enabled.

Written by the indexing model from the issue text.