Unmute YAML REST test

Author: PeteGillinElastic

x-pack/qa/multi-project/xpack-rest-tests-with-multiple-projects/build.gradle

@@ -49,7 +49,6 @@ tasks.named("yamlRestTest").configure {
     '^ilm/10_basic/Test Undeletable Policy In Use',
     '^ilm/20_move_to_step/*',
     '^ilm/30_retry/*',
-    '^ilm/40_explain_lifecycle/*',
     '^ilm/60_operation_mode/*',
     '^ilm/60_remove_policy_for_index/*',
     '^ilm/70_downsampling/*',