chore: increase parallelism of TestWorkspaceQuota (#6710)

This does a lot of build operations, so having multiple provisioner
daemons is great.

We were actually approaching the ceiling here for test duration!

coderd/database/errors.go

@@ -6,6 +6,14 @@ import (
 	"github.com/lib/pq"
 )
 
+func IsSerializedError(err error) bool {
+	var pqErr *pq.Error
+	if errors.As(err, &pqErr) {
+		return pqErr.Code.Name() == "serialization_failure"
+	}
+	return false
+}
+
 // IsUniqueViolation checks if the error is due to a unique violation.
 // If one or more specific unique constraints are given as arguments,
 // the error must be caused by one of them. If no constraints are given,