Re-enable the optimization for boost > 1.86

Summary:
The bug with `boost::container::flat_map::extract_sequence` has been fixed (see boostorg/container#288)
This should go out in boost 1.87 (probably in a few months).

Therefore, let's re-enable the optimization for boost versions != 1.86

Reviewed By: arnaudvenet

Differential Revision: D62436361

fbshipit-source-id: b2010fbae81f4b65039ee1dd6459c5e7021dbc3f

include/sparta/FlatMap.h

@@ -280,7 +280,7 @@ class FlatMap final
       break;
     }
     default: {
-#if (BOOST_VERSION / 100) >= 1086
+#if (BOOST_VERSION / 100) == 1086
       // TODO(T200541423): Boost 1.86.0 has a bug with `extract_sequence()` and
       // `adopt_sequence`. Let's disable the optimization for now. See
       // https://github.com/boostorg/container/issues/288