c/bmaas/bmdb: fix flaky parallel test

We weren't handling an expected error properly, which sometimes just
pops up in normal operation.

Change-Id: I45f3011236fbce41dc5e139e39f60c0002fd6cec
Reviewed-on: https://review.monogon.dev/c/monogon/+/1366
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/cloud/bmaas/bmdb/sessions_test.go b/cloud/bmaas/bmdb/sessions_test.go
index bd29d5d..f3977d5 100644
--- a/cloud/bmaas/bmdb/sessions_test.go
+++ b/cloud/bmaas/bmdb/sessions_test.go
@@ -497,6 +497,9 @@
 		for {
 			err := workOnce(ctxS, workerID, session)
 			if err != nil {
+				if errors.Is(err, ErrNothingToDo) {
+					continue
+				}
 				if errors.Is(err, ctxS.Err()) {
 					return
 				}