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/dbtestutil/db.go

@@ -135,7 +135,8 @@ func NewDB(t testing.TB, opts ...Option) (database.Store, pubsub.Pubsub) {
 		if o.dumpOnFailure {
 			t.Cleanup(func() { DumpOnFailure(t, connectionURL) })
 		}
-		db = database.New(sqlDB)
+		// Unit tests should not retry serial transaction failures.
+		db = database.New(sqlDB, database.WithSerialRetryCount(1))
 
 		ps, err = pubsub.New(context.Background(), o.logger, sqlDB, connectionURL)
 		require.NoError(t, err)