transactions_block_ddl.js tests that open transactions block ddl operations on the involved collections. Until recently this test was blocked from running in sharded environments due to SERVER-84330, but upon unblocking the tests it was found that some ddl operations show up differently in $currOp on unsharded and sharded clusters. 

For example, for this test a collection drop shows up as 

"command" : drop

 in an unsharded environment but as 

"command" : _shardsvrDropCollection

 in a sharded environment. From the test, we know these differences also exist for a database drop, a collection rename within the same database and a collection rename between two different databases. 

We should either reconcile these differences in $currOp or change the test reflect this.