chore: fix concurrent CommitQuota transactions for unrelated users/orgs (#15261)

The failure condition being fixed is `w1` and `w2` could belong
to different users, organizations, and templates and still cause a
serializable failure if run concurrently. This is because the old query 
did a `seq scan` on the `workspace_builds` table. Since that is the 
table being updated, we really want to prevent that.

So before this would fail for any 2 workspaces. Now it only fails if
`w1` and `w2` are owned by the same user and organization.

coderd/database/dbgen/dbgen.go

@@ -408,6 +408,8 @@ func OrganizationMember(t testing.TB, db database.Store, orig database.Organizat
 }
 
 func Group(t testing.TB, db database.Store, orig database.Group) database.Group {
+	t.Helper()
+
 	name := takeFirst(orig.Name, testutil.GetRandomName(t))
 	group, err := db.InsertGroup(genCtx, database.InsertGroupParams{
 		ID:             takeFirst(orig.ID, uuid.New()),