fix: Set MAX_DB_WORKER limit in local_run

We allow the user to set the number of concurrent jobs using the
`--concurrency` argument and use this to update the worker limit, but we
didn't update the database worker limit.

The distinction is meaningless for local jobs in any case because these
jobs are just generating dummy data, but it meant that jobs ran with
less parallelism than expected. It also lead to "Waiting on available
database workers" messages appearing in the log output which caused
confusion and anxiety.

jobrunner/cli/local_run.py

@@ -259,6 +259,7 @@ def create_and_run_jobs(
     config.USING_DUMMY_DATA_BACKEND = True
     config.CLEAN_UP_DOCKER_OBJECTS = clean_up_docker_objects
     config.MAX_WORKERS = concurrency
+    config.MAX_DB_WORKERS = concurrency
     config.DEFAULT_JOB_MEMORY_LIMIT = memory
     config.DEFAULT_JOB_CPU_COUNT = cpus