MDEV-28709 unexpected X lock on Supremum in READ COMMITTED

Post-push fix. The flag of transaction which indicates that it's necessary
to forbid gap lock inheritance after XA PREPARE could be inverted if
lock_release_on_prepare_try() is invoked several times. The fix is to
toggle it on lock_release_on_prepare() exit.

storage/innobase/lock/lock0lock.cc

@@ -4116,14 +4116,15 @@ static bool lock_release_on_prepare_try(trx_t *trx)
 
   lock_sys.rd_unlock();
   trx->mutex_unlock();
-  trx->set_skip_lock_inheritance();
   return all_released;
 }
 
 /** Release non-exclusive locks on XA PREPARE,
 and release possible other transactions waiting because of these locks. */
 void lock_release_on_prepare(trx_t *trx)
 {
+  auto _ = make_scope_exit([trx]() { trx->set_skip_lock_inheritance(); });
+
   for (ulint count= 5; count--; )
     if (lock_release_on_prepare_try(trx))
       return;