Use the cheapest default token when multiple are available (#2990)

Previously we would just use the first one we found. This is a valid
behavior, but we want to change it so that we apply the cheapest default
if multiple are available (this way we avoid having to go back after the
fact and give refunds).

db/src/test/java/google/registry/sql/flyway/FlywayDeadlockTest.java

@@ -178,8 +178,7 @@ public class FlywayDeadlockTest {
                   .filter(line -> !line.isBlank())
                   .collect(joining(" ")))
           .map(FlywayDeadlockTest::getDdlLockedElementName)
-          .filter(Optional::isPresent)
-          .map(Optional::get)
+          .flatMap(Optional::stream)
           .collect(toImmutableSet());
     } catch (IOException e) {
       throw new RuntimeException(e);