Unchecked dynamic_cast

If the dynamic_cast fails, a null pointer dereference will occur; if the dynamic_cast cannot fail, using static_cast instead offers better performance. Dynamic_cast may fail and return null if the type cast is incompatible
/src/mongo/db/modules/enterprise/src/search/mongot_cursor.cpp:100: FORWARD_NULL 121640 Dynamic cast to pointer "dynamic_cast <mongo::DocumentSourceInternalSearchMongotRemote *>(potentialSearchStage.get())" can return "NULL".
/src/mongo/db/modules/enterprise/src/search/mongot_cursor.cpp:100: FORWARD_NULL 121640 Assigning: "origSearchStage" = "dynamic_cast <mongo::DocumentSourceInternalSearchMongotRemote *>(potentialSearchStage.get())".